Decoder, encoder, and decoding method

ABSTRACT

Method, device, apparatus, and computer-readable storage medium to determine whether video block is a fractional boundary video block (See paragraph [0032] and FIG.  7 .) and to partition the fractional boundary video block into inferred partitions using a subset of available partition modes (See paragraph [0033] and FIG.  8 .) are disclosed.

TECHNICAL FIELD

This disclosure relates to video coding and more particularly totechniques for partitioning a picture of video data.

BACKGROUND ART

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, laptop or desktop computers,tablet computers, digital recording devices, digital media players,video gaming devices, cellular telephones, including so-calledsmartphones, medical imaging devices, and the like. Digital video may becoded according to a video coding standard. Video coding standards mayincorporate video compression techniques. Examples of video codingstandards include ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known asISO/IEC MPEG-4 AVC) and High-Efficiency Video Coding (HEVC). HEVC isdescribed in High Efficiency Video Coding (HEVC), Rec. ITU-T H.265,December 2016, which is incorporated by reference, and referred toherein as ITU-T H.265. Extensions and improvements for ITU-T H.265 arecurrently being considered for the development of next generation videocoding standards. For example, the ITU-T Video Coding Experts Group(VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG) (collectivelyreferred to as the Joint Video Exploration Team (JVET)) are studying thepotential need for standardization of future video coding technologywith a compression capability that significantly exceeds that of thecurrent HEVC standard. The Joint Exploration Model 7 (JEM 7), AlgorithmDescription of Joint Exploration Test Model 7 (JEM 7), ISO/IECJTC1/SC29/WG11 Document: JVET-G1001, July 2017, Torino, IT, which isincorporated by reference herein, describes the coding features that areunder coordinated test model study by the JVET as potentially enhancingvideo coding technology beyond the capabilities of ITU-T H.265. Itshould be noted that the coding features of JEM 7 are implemented in JEMreference software. As used herein, the term JEM may collectively referto algorithms included in JEM 7 and implementations of JEM referencesoftware.

Video compression techniques enable data requirements for storing andtransmitting video data to be reduced. Video compression techniques mayreduce data requirements by exploiting the inherent redundancies in avideo sequence. Video compression techniques may sub-divide a videosequence into successively smaller portions (i.e., groups of frameswithin a video sequence, a frame within a group of frames, slices withina frame, coding tree units (e.g., macroblocks) within a slice, codingblocks within a coding tree unit, etc.). Intra prediction codingtechniques (e.g., intra-picture (spatial)) and inter predictiontechniques (i.e., inter-picture (temporal)) may be used to generatedifference values between a unit of video data to be coded and areference unit of video data. The difference values may be referred toas residual data. Residual data may be coded as quantized transformcoefficients. Syntax elements may relate residual data and a referencecoding unit (e.g., intra-prediction mode indices, motion vectors, andblock vectors). Residual data and syntax elements may be entropy coded.Entropy encoded residual data and syntax elements may be included in acompliant bitstream.

SUMMARY OF INVENTION

In one example, a method of partitioning video data for video coding,comprises receiving a video block including sample values, determiningwhether the video block is a fractional boundary video block andpartitioning the sample values according to an inferred partitioningusing a subset of available partition modes.

In one example, a method of reconstructing video data comprisesreceiving residual data corresponding to a coded video block includingsample values, determining whether the coded video block is a fractionalboundary video block, determining a partitioning for the coded videoblock according to an inferred partitioning using a subset of availablepartition modes, and reconstructing video data based on the residualdata and the partitioning for the coded video block.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example of a group ofpictures coded according to a quad tree binary tree partitioning inaccordance with one or more techniques of this disclosure.

FIG. 2 is a conceptual diagram illustrating an example of a quad treebinary tree in accordance with one or more techniques of thisdisclosure.

FIG. 3 is a conceptual diagram illustrating video component quad treebinary tree partitioning in accordance with one or more techniques ofthis disclosure.

FIG. 4 is a conceptual diagram illustrating an example of a videocomponent sampling format in accordance with one or more techniques ofthis disclosure.

FIG. 5 is a conceptual diagram illustrating possible coding structuresfor a block of video data according to one or more techniques of thisdisclosure.

FIG. 6A is a conceptual diagram illustrating an example of coding ablock of video data in accordance with one or more techniques of thisdisclosure.

FIG. 6B is a conceptual diagram illustrating an example of coding ablock of video data in accordance with one or more techniques of thisdisclosure.

FIG. 7 is a conceptual diagram illustrating an example of a picturepartitioned into coding units in accordance with one or more techniquesof this disclosure.

FIG. 8 is a conceptual diagram illustrating examples of quad treepartitioning for coding units occurring at picture boundaries inaccordance with one or more techniques of this disclosure.

FIG. 9 is a conceptual diagram illustrating partitioning modes inaccordance with one or more techniques of this disclosure.

FIG. 10 is a conceptual diagram illustrating partitioning modes inaccordance with one or more techniques of this disclosure.

FIG. 11 is a conceptual diagram illustrating partitioning modes inaccordance with one or more techniques of this disclosure.

FIG. 12 is a block diagram illustrating an example of a system that maybe configured to encode and decode video data according to one or moretechniques of this disclosure.

FIG. 13 is a block diagram illustrating an example of a video encoderthat may be configured to encode video data according to one or moretechniques of this disclosure.

FIG. 14A is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 14B is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 14C is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 15A is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 15B is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 15C is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 16A is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 16B is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 16C is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 17A is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 17B is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 17C is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 17D is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 18A is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 18B is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 18C is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 18D is a conceptual diagram illustrating an example of partitioningfor coding units occurring at picture boundaries in accordance with oneor more techniques of this disclosure.

FIG. 19 is a block diagram illustrating an example of a video decoderthat may be configured to decode video data according to one or moretechniques of this disclosure.

FIG. 20 includes conceptual diagrams illustrating examples ofpartitioning for coding units occurring at picture boundaries inaccordance with one or more techniques of this disclosure.

FIG. 21 includes a conceptual diagram illustrating examples ofpartitioning for coding units occurring at picture boundaries inaccordance with one or more techniques of this disclosure.

FIG. 22 includes a conceptual diagram illustrating examples ofpartitioning for coding units occurring at picture boundaries inaccordance with one or more techniques of this disclosure.

FIG. 23 includes a conceptual diagram illustrating examples ofpartitioning for coding units occurring at picture boundaries inaccordance with one or more techniques of this disclosure.

FIG. 24 includes a conceptual diagram illustrating examples ofpartitioning for coding units occurring at picture boundaries inaccordance with one or more techniques of this disclosure.

DESCRIPTION OF EMBODIMENTS

In general, this disclosure describes various techniques for codingvideo data. In particular, this disclosure describes techniques forpartitioning a picture of video data. It should be noted that althoughtechniques of this disclosure are described with respect to ITU-T H.264,ITU-T H.265, and JEM, the techniques of this disclosure are generallyapplicable to video coding. For example, the coding techniques describedherein may be incorporated into video coding systems, (including videocoding systems based on future video coding standards) including blockstructures, intra prediction techniques, inter prediction techniques,transform techniques, filtering techniques, and/or entropy codingtechniques other than those included in ITU-T H.265 and JEM. Thus,reference to ITU-T H.264, ITU-T H.265, and/or JEM is for descriptivepurposes and should not be construed to limit the scope of thetechniques described herein. Further, it should be noted thatincorporation by reference of documents herein is for descriptivepurposes and should not be construed to limit or create ambiguity withrespect to terms used herein. For example, in the case where anincorporated reference provides a different definition of a term thananother incorporated reference and/or as the term is used herein, theterm should be interpreted in a manner that broadly includes eachrespective definition and/or in a manner that includes each of theparticular definitions in the alternative.

In one example, a device for partitioning video data for video codingcomprises one or more processors configured to receive a video blockincluding sample values, determine whether the video block is afractional boundary video block and partition the sample valuesaccording to an inferred partitioning using a subset of availablepartition modes.

In one example, a non-transitory computer-readable storage mediumcomprises instructions stored thereon that, when executed, cause one ormore processors of a device to receive a video block including samplevalues, determine whether the video block is a fractional boundary videoblock, and partition the sample values according to an inferredpartitioning using a subset of available partition modes.

In one example, an apparatus comprises means for receiving a video blockincluding sample values, means for determining whether the video blockis a fractional boundary video block and means for partitioning thesample values according to an inferred partitioning using a subset ofavailable partition modes.

In one example, a device for reconstructing video data comprises one ormore processors configured to receive residual data corresponding to acoded video block including sample values, determine whether the codedvideo block is a fractional boundary video block, determine apartitioning for the coded video block according to an inferredpartitioning using a subset of available partition modes, andreconstruct video data based on the residual data and the partitioningfor the coded video block.

In one example, a non-transitory computer-readable storage mediumcomprises instructions stored thereon that, when executed, cause one ormore processors of a device to receive residual data corresponding to acoded video block including sample values, determine whether the codedvideo block is a fractional boundary video block, determine apartitioning for the coded video block according to an inferredpartitioning using a subset of available partition modes, andreconstruct video data based on the residual data and the partitioningfor the coded video block.

In one example, an apparatus comprises means for receiving residual datacorresponding to a coded video block including sample values, means fordetermining whether the coded video block is a fractional boundary videoblock, means for determining a partitioning for the coded video blockaccording to an inferred partitioning using a subset of availablepartition modes, and means for reconstructing video data based on theresidual data and the partitioning for the coded video block.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

Video content typically includes video sequences comprised of a seriesof frames (or pictures). A series of frames may also be referred to as agroup of pictures (GOP). Each video frame or picture may include aplurality of slices or tiles, where a slice or tile includes a pluralityof video blocks. As used herein, the term video block may generallyrefer to an area of a picture or may more specifically refer to thelargest array of sample values that may be predictively coded,sub-divisions thereof, and/or corresponding structures. Further, theterm current video block may refer to an area of a picture being encodedor decoded. A video block may be defined as an array of sample valuesthat may be predictively coded. It should be noted that in some casespixel values may be described as including sample values for respectivecomponents of video data, which may also be referred to as colorcomponents, (e.g., luma (Y) and chroma (Cb and Cr) components or red,green, and blue components). It should be noted that in some cases, theterms pixel value and sample value are used interchangeably. Videoblocks may be ordered within a picture according to a scan pattern(e.g., a raster scan). A video encoder may perform predictive encodingon video blocks and sub-divisions thereof. Video blocks andsub-divisions thereof may be referred to as nodes.

ITU-T H.264 specifies a macroblock including 16×16 luma samples. Thatis, in ITU-T H.264, a picture is segmented into macroblocks. ITU-T H.265specifies an analogous Coding Tree Unit (CTU) structure, which is alsoreferred to as a largest coding unit (LCU). In ITU-T H.265, pictures aresegmented into CTUs. In ITU-T H.265, for a picture, a CTU size may beset as including one of 16×16, 32×32, or 64×64 luma samples. In ITU-TH.265, a CTU is composed of respective Coding Tree Blocks (CTB) for eachcomponent of video data (e.g., luma (Y) and chroma (Cb and Cr). Further,in ITU-T H.265, a CTU may be partitioned according to a quadtree (QT)partitioning structure, which results in the CTBs of the CTU beingpartitioned into Coding Blocks (CB). That is, in ITU-T H.265, a CTU maybe partitioned into quadtree leaf nodes. According to ITU-T H.265, oneluma CB together with two corresponding chroma CBs and associated syntaxelements are referred to as a coding unit (CU). In ITU-T H.265, aminimum allowed size of a CB may be signaled. In ITU-T H.265, thesmallest minimum allowed size of a luma CB is 8×8 luma samples. In ITU-TH.265, the decision to code a picture area using intra prediction orinter prediction is made at the CU level.

In ITU-T H.265, a CU is associated with a prediction unit (PU) structurehaving its root at the CU. In ITU-T H.265, PU structures allow luma andchroma CBs to be split for purposes of generating correspondingreference samples. That is, in ITU-T H.265, luma and chroma CBs may besplit into respect luma and chroma prediction blocks (PBs), where a PBincludes a block of sample values for which the same prediction isapplied. In ITU-T H.265, a CB may be partitioned into 1, 2, or 4 PBs.ITU-T H.265 supports PB sizes from 64×64 samples down to 4×4 samples. InITU-T H.265, square PBs are supported for intra prediction, where a CBmay form the PB or the CB may be split into four square PBs (i.e., intraprediction PB types include M×M or M/2×M/2, where M is the height andwidth of the square CB). In ITU-T H.265, in addition to the square PBs,rectangular PBs are supported for inter prediction, where a CB may byhalved vertically or horizontally to form PBs (i.e., inter prediction PBtypes include M×M, M/2×M/2, M/2×M, or M×M/2). Further, it should benoted that in ITU-T H.265, for inter prediction, four asymmetric PBpartitions are supported, where the CB is partitioned into two PBs atone quarter of the height (at the top or the bottom) or width (at theleft or the right) of the CB (i.e., asymmetric partitions include M/4×Mleft, M/4×M right, M×M/4 top, and M×M/4 bottom). Intra prediction data(e.g., intra prediction mode syntax elements) or inter prediction data(e.g., motion data syntax elements) corresponding to a PB is used toproduce reference and/or predicted sample values for the PB.

JEM specifies a CTU having a maximum size of 256×256 luma samples. JEMspecifies a quadtree plus binary tree (QTBT) block structure. In JEM,the QTBT structure enables quadtree leaf nodes to be further partitionedby a binary tree (BT) structure. That is, in JEM, the binary treestructure enables quadtree leaf nodes to be recursively dividedvertically or horizontally. FIG. 1 illustrates an example of a CTU(e.g., a CTU having a size of 256×256 luma samples) being partitionedinto quadtree leaf nodes and quadtree leaf nodes being furtherpartitioned according to a binary tree. That is, in FIG. 1 dashed linesindicate additional binary tree partitions in a quadtree. Thus, thebinary tree structure in JEM enables square and rectangular leaf nodes,where each leaf node includes a CB. As illustrated in FIG. 1, a pictureincluded in a GOP may include slices, where each slice includes asequence of CTUs and each CTU may be partitioned according to a QTBTstructure. FIG. 1 illustrates an example of QTBT partitioning for oneCTU included in a slice. FIG. 2 is a conceptual diagram illustrating anexample of a QTBT corresponding to the example QTBT partitionillustrated in FIG. 1. In JEM, a QTBT is signaled by signaling QT splitflag and BT split mode syntax elements. When a QT split flag has a valueof 1, a QT split is indicated. When a QT split flag has a value of 0, aBT split mode syntax element is signaled. When a BT split mode syntaxelement has a value of 0 (i.e., BT split mode coding tree =0), no binarysplitting is indicated. When a BT split mode syntax element has a valueof 1, a vertical split mode is indicated. When a BT split mode syntaxelement has a value of 2, a horizontal split mode is indicated. Further,BT splitting may be performed until a maximum BT depth is reached.

In FIG. 2, Q indicates a quadtree split, H indicates a horizontal binarysplit, V indicates a vertical binary split, and CU indicates a resultingCU leaf. As illustrated in FIG. 2, split indicators (e.g., QT split flagsyntax elements and BT split mode syntax elements) are associated with adepth, where a depth of zero corresponds to a root of a QTBT and higherdepth values correspond to subsequent depths beyond the root. It shouldbe noted that in FIG. 2, the tree corresponds to a left-to-right z-scan.That is, for QT splits, tree nodes from left-to-right in the graphcorrespond to z-scan of the QT parts, for horizontal splits, tree nodesfrom left-to-right correspond to upper-to-lower scan of the parts, andfor vertical splits, tree nodes from left-to-right correspond toleft-to-right scan of the parts. Other example trees described hereinmay also utilize a left-to-right z-scan.

Further, it should be noted that in JEM, luma and chroma components mayhave separate QTBT partitions. That is, in JEM luma and chromacomponents may be partitioned independently by signaling respectiveQTBTs. FIG. 3 illustrates an example of a CTU being partitionedaccording to a QTBT for a luma component and an independent QTBT forchroma components. As illustrated in FIG. 3, when independent QTBTs areused for partitioning a CTU, CBs of the luma component are not requiredto and do not necessarily align with CBs of chroma components.Currently, in JEM independent QTBT structures are enabled for slicesusing intra prediction techniques. It should be noted that in somecases, values of chroma variables may need to be derived from theassociated luma variable values. In these cases, the sample position inchroma and chroma format may be used to determine the correspondingsample position in luma to determine the associated luma variable value.

Additionally, it should be noted that JEM includes the followingparameters for signaling of a QTBT tree:

CTU size: the root node size of a quadtree. (e.g., 256×256, 128×128,64×64, 32×32, 16×16 luma samples);

MinQTSize: the minimum allowed quadtree leaf node size (e.g., 16×16, 8×8luma samples);

MaxBTSize: the maximum allowed binary tree root node size, i.e., themaximum size of a leaf quadtree node that may be partitioned by binarysplitting (e.g., 64×64 luma samples);

MaxBTDepth: the maximum allowed binary tree depth, i.e., the lowestlevel at which binary splitting may occur, where the quadtree leaf nodeis the root (e.g., 3);

MinBTSize: the minimum allowed binary tree leaf node size; the minimumwidth or height of a binary leaf node (e.g., 4 luma samples).

It should be noted that in some examples, MinQTSize, MaxBTSize,MaxBTDepth, and/or MinBTSize may be different for the differentcomponents of video.

In JEM, CBs are used for prediction without any further partitioning.That is, in JEM, a CB may be a block of sample values on which the sameprediction is applied. Thus, a JEM QTBT leaf node may be analogous a PBin ITU-T H.265.

A video sampling format, which may also be referred to as a chromaformat, may define the number of chroma samples included in a CU withrespect to the number of luma samples included in a CU. For example, forthe 4:2:0 sampling format, the sampling rate for the luma component istwice that of the chroma components for both the horizontal and verticaldirections. As a result, for a CU formatted according to the 4:2:0format, the width and height of an array of samples for the lumacomponent are twice that of each array of samples for the chromacomponents. FIG. 4 is a conceptual diagram illustrating an example of acoding unit formatted according to a 4:2:0 sample format. FIG. 4illustrates the relative position of chroma samples with respect to lumasamples within a CU. As described above, a CU is typically definedaccording to the number of horizontal and vertical luma samples. Thus,as illustrated in FIG. 4, a 16×16 CU formatted according to the 4:2:0sample format includes 16×16 samples of luma components and 8×8 samplesfor each chroma component. Further, in the example illustrated in FIG.4, the relative position of chroma samples with respect to luma samplesfor video blocks neighboring the 16×16 CU are illustrated. For a CUformatted according to the 4:2:2 format, the width of an array ofsamples for the luma component is twice that of the width of an array ofsamples for each chroma component, but the height of the array ofsamples for the luma component is equal to the height of an array ofsamples for each chroma component. Further, for a CU formatted accordingto the 4:4:4 format, an array of samples for the luma component has thesame width and height as an array of samples for each chroma component.

As described above, intra prediction data or inter prediction data isused to produce reference sample values for a block of sample values.The difference between sample values included in a current PB, oranother type of picture area structure, and associated reference samples(e.g., those generated using a prediction) may be referred to asresidual data. Residual data may include respective arrays of differencevalues corresponding to each component of video data. Residual data maybe in the pixel domain. A transform, such as, a discrete cosinetransform (DCT), a discrete sine transform (DST), an integer transform,a wavelet transform, or a conceptually similar transform, may be appliedto an array of difference values to generate transform coefficients. Itshould be noted that in ITU-T H.265, a CU is associated with a transformunit (TU) structure having its root at the CU level. That is, in ITU-TH.265, an array of difference values may be sub-divided for purposes ofgenerating transform coefficients (e.g., four 8×8 transforms may beapplied to a 16×16 array of residual values). For each component ofvideo data, such sub-divisions of difference values may be referred toas Transform Blocks (TBs). It should be noted that in ITU-T H.265, TBsare not necessarily aligned with PBs. FIG. 5 illustrates examples ofalternative PB and TB combinations that may be used for coding aparticular CB. Further, it should be noted that in ITU-T H.265, TBs mayhave the following sizes 4×4, 8×8, 16×16, and 32×32.

It should be noted that in JEM, residual values corresponding to a CBare used to generate transform coefficients without furtherpartitioning. That is, in JEM a QTBT leaf node may be analogous to botha PB and a TB in ITU-T H.265. It should be noted that in JEM, a coretransform and a subsequent secondary transforms may be applied (in thevideo encoder) to generate transform coefficients. For a video decoder,the order of transforms is reversed. Further, in JEM, whether asecondary transform is applied to generate transform coefficients may bedependent on a prediction mode.

A quantization process may be performed on transform coefficients.Quantization essentially scales transform coefficients in order to varythe amount of data required to represent a group of transformcoefficients. Quantization may generally include division of transformcoefficients by a quantization scaling factor and any associatedrounding functions (e.g., rounding to the nearest integer). Quantizedtransform coefficients may be referred to as coefficient level values.Inverse quantization (or “dequantization”) may include multiplication ofcoefficient level values by the quantization scaling factor. It shouldbe noted that as used herein the term quantization process in someinstances may refer to division by a scaling factor to generate levelvalues and multiplication by a scaling factor to recover transformcoefficients in some instances. That is, a quantization process mayrefer to quantization in some cases and inverse quantization in somecases.

FIGS. 6A-6B are conceptual diagrams illustrating examples of coding ablock of video data. As illustrated in FIG. 6A, a current block of videodata (e.g., a CB corresponding to a video component) is encoded bygenerating a residual by subtracting a set of prediction values from thecurrent block of video data, performing a transformation on theresidual, and quantizing the transform coefficients to generate levelvalues. As illustrated in FIG. 6B, the current block of video data isdecoded by performing inverse quantization on level values, performingan inverse transform, and adding a set of prediction values to theresulting residual. It should be noted that in the examples in FIGS.6A-6B, the sample values of the reconstructed block differs from thesample values of the current video block that is encoded. In thismanner, coding may said to be lossy. However, the difference in samplevalues may be considered acceptable or imperceptible to a viewer of thereconstructed video. Further, as illustrated in FIGS. 6A-6B, scaling isperformed using an array of scaling factors.

As illustrated in FIG. 6A, quantized transform coefficients are codedinto a bitstream. Quantized transform coefficients and syntax elements(e.g., syntax elements indicating a coding structure for a video block)may be entropy coded according to an entropy coding technique. Examplesof entropy coding techniques include content adaptive variable lengthcoding (CAVLC), context adaptive binary arithmetic coding (CABAC),probability interval partitioning entropy coding (PIPE), and the like.Entropy encoded quantized transform coefficients and correspondingentropy encoded syntax elements may form a compliant bitstream that canbe used to reproduce video data at a video decoder. An entropy codingprocess may include performing a binarization on syntax elements.Binarization refers to the process of converting a value of a syntaxvalue into a series of one or more bits. These bits may be referred toas “bins.” Binarization is a lossless process and may include one or acombination of the following coding techniques: fixed length coding,unary coding, truncated unary coding, truncated Rice coding, Golombcoding, k-th order exponential Golomb coding, and Golomb-Rice coding.For example, binarization may include representing the integer value of5 for a syntax element as 00000101 using an 8-bit fixed lengthbinarization technique or representing the integer value of 5 as 11110using a unary coding binarization technique. As used herein each of theterms fixed length coding, unary coding, truncated unary coding,truncated Rice coding, Golomb coding, k-th order exponential Golombcoding, and Golomb-Rice coding may refer to general implementations ofthese techniques and/or more specific implementations of these codingtechniques. For example, a Golomb-Rice coding implementation may bespecifically defined according to a video coding standard, for example,ITU-T H.265. An entropy coding process further includes coding binvalues using lossless data compression algorithms. In the example of aCABAC, for a particular bin, a context model may be selected from a setof available context models associated with the bin. In some examples, acontext model may be selected based on a previous bin and/or values ofprevious syntax elements. A context model may identify the probabilityof a bin having a particular value. For instance, a context model mayindicate a 0.7 probability of coding a 0-valued bin and a 0.3probability of coding a 1-valued bin. It should be noted that in somecases the probability of coding a 0-valued bin and probability of codinga 1-valued bin may not sum to 1. After selecting an available contextmodel, a CABAC entropy encoder may arithmetically code a bin based onthe identified context model. The context model may be updated based onthe value of a coded bin. The context model may be updated based on anassociated variable stored with the context, e.g., adaptation windowsize, number of bins coded using the context. It should be noted, thataccording to ITU-T H.265, a CABAC entropy encoder may be implemented,such that some syntax elements may be entropy encoded using arithmeticencoding without the usage of an explicitly assigned context model, suchcoding may be referred to as bypass coding.

As described above, intra prediction data or inter prediction data mayassociate an area of a picture (e.g., a PB or a CB) with correspondingreference samples. For intra prediction coding, an intra prediction modemay specify the location of reference samples within a picture. In ITU-TH.265, defined possible intra prediction modes include a planar (i.e.,surface fitting) prediction mode (predMode: 0), a DC (i.e., flat overallaveraging) prediction mode (predMode: 1), and 33 angular predictionmodes (predMode: 2-34). In JEM, defined possible intra-prediction modesinclude a planar prediction mode (predMode: 0), a DC prediction mode(predMode: 1), and 65 angular prediction modes (predMode: 2-66). Itshould be noted that planar and DC prediction modes may be referred toas non-directional prediction modes and that angular prediction modesmay be referred to as directional prediction modes. It should be notedthat the techniques described herein may be generally applicableregardless of the number of defined possible prediction modes.

For inter prediction coding, a motion vector (MV) identifies referencesamples in a picture other than the picture of a video block to be codedand thereby exploits temporal redundancy in video. For example, acurrent video block may be predicted from reference block(s) located inpreviously coded frame(s) and a motion vector may be used to indicatethe location of the reference block. A motion vector and associated datamay describe, for example, a horizontal component of the motion vector,a vertical component of the motion vector, a resolution for the motionvector (e.g., one-quarter pixel precision, one-half pixel precision,one-pixel precision, two-pixel precision, four-pixel precision), aprediction direction and/or a reference picture index value. Further, acoding standard, such as, for example ITU-T H.265, may support motionvector prediction. Motion vector prediction enables a motion vector tobe specified using motion vectors of neighboring blocks. Examples ofmotion vector prediction include advanced motion vector prediction(AMVP), temporal motion vector prediction (TMVP), so-called “merge”mode, and “skip” and “direct” motion inference. Further, JEM supportsadvanced temporal motion vector prediction (ATMVP) and Spatial-temporalmotion vector prediction (STMVP).

As described above, during video coding, a picture may be segmented orpartitioned into a basic coding unit, e.g., 16×16 marcoblocks in ITU-TH.264; 16×16, 32×32, or 64×64 CTUs in H.265; and 16×16, 32×32, 64×64,128×128, or 256×256 CTUs in JEM. Video sequences may have various videoproperties including, for example, frame rates and picture resolutions.For example, so-called high-definition (HD) video sequences may includepictures having resolutions of 1980×1080 pixels or 1280×720 pixels.Further, example so-called ultra-high-definition (UHD) video sequencesmay include pictures having resolutions of 3840×2160 pixels or 7680×4320pixels. Further, video sequences include pictures having various otherresolutions. Thus, in some cases, depending on the size of a picture andthe size of a basic coding unit (e.g., CTU size), the width and/orheight of a picture may not be divisible into an integer number of basiccoding units. FIG. 7 illustrates an example of a 1280×720 picturepartitioned into 64×64 CTUs. As illustrated in FIG. 7, the bottom row ofCTUs does not align with the bottom picture boundary. That is, only 16rows of samples in the bottom row CTUs fit within the picture boundary(720 divided by 64 is 11 with a remainder of 16). As used herein, theterm, fractional boundary video block, fractional boundary CTU,fractional boundary LCU, or fractional boundary coding unit may be usedto refer to a video block in a boundary column and/or row of a picturehaving only a portion thereof within the picture boundary. It should benoted that boundary columns and boundary rows may include slice, tile,and/or picture boundaries. Further, it should be noted that in somecases, (e.g., omnidirectional video or so-called wraparound video), aboundary columns may include a left boundary and a boundary row mayinclude a top row.

Typically, for example, in ITU-T H.265, fractional boundary video blocksare partitioned in a predefined manner, that is, an inferredpartitioning occurs without signaling split indicators. Typically, aninferred partitioning is a partitioning that occurs to the depth whereCUs that align with the picture boundary are formed. For example,referring to FIG. 7, an inferred partitioning of a bottom row CTU mayinclude an inferred QT partitioning resulting in a row of four 16×16 CUsat the top of the CTU, where the row of four 16×16 CUs is includedwithin the picture boundary. FIG. 8 is a conceptual diagram illustratingexamples of inferred QT partitions for example fractional boundary videoblocks. It should be noted that in FIG. 8 X's correspond to nodesresulting from a partition that are outside of the picture boundary.Referring to the example illustrated in FIG. 8, the partitioning of theCTU₁ may correspond to the described example inferred partitioning of abottom row CTU in FIG. 7. It should be noted that in some examples, theCUs within the picture boundary resulting from an inferred partitioningmay be further partitioned. For example, referring to the CTU₀ in FIG.8, in some examples, the six CUs of the CTU within vertical pictureboundary may be further partitioned.

It should be noted, as illustrated in FIG. 8, that partitioningfractional boundary video blocks in a predefined manner may result in arelatively large number of relatively small video blocks (e.g., CUs)occurring at or near a picture boundary. Having a relatively largenumber of relatively small video blocks occurring at or near a pictureboundary may adversely impact coding efficiency, due to each video blockrequiring the transmission/parsing of syntax elements associated withthe video block coding structure. For example, as described above, inITU-T H.265, a CU forms the root of a PU and TU and thus each CU isassociated with PU and TU coding structures (i.e., semantics and syntaxelements).

Further, it should be noted that with respect to JEM, techniques havebeen proposed for partitioning CUs according to asymmetric binary treepartitioning. F. Le Leannec, et al., “Asymmetric Coding Units in QTBT,”4th Meeting: Chengdu, CN, 15-21 Oct. 2016, Doc. JVET-D0064 (hereinafter“Le Leannec”), describes where in addition to the symmetric vertical andhorizontal BT split modes, four additional asymmetric BT split modes aredefined. In Le Leannec, the four additionally defined BT split modes fora CU include: horizontal partitioning at one quarter of the height (atthe top for one mode or at the bottom for one mode) or verticalpartitioning at one quarter of the width (at the left for one mode orthe right for one mode). The four additionally defined BT split modes inLe Leannec are illustrated in FIG. 9 as Hor_Up, Hor_Down, Ver_Left, andVer_Right.

Further, Li, et al., “Multi-Type-Tree,” 4th Meeting: Chengdu, CN, 15-21Oct. 2016, Doc. JVET-D0117r1 (hereinafter “Li”), describes an examplewhere in addition to the symmetric vertical and horizontal BT splitmodes, two additional triple tree (TT) split modes are defined. Itshould be noted that partitioning a node into three blocks about adirection may be referred to as triple tree (TT) partitioning. Thus,split types may include horizontal and vertical binary splits andhorizontal and vertical TT splits. In Li, the two additionally definedTT split modes for a node include: (1) horizontal TT partitioning at onequarter of the height from the top edge and the bottom edge of a node;and (2) vertical TT partitioning at one quarter of the width from theleft edge and the right edge of a node. The two additionally defined TTsplit modes in Li are illustrated in FIG. 9 as Vertical TT andHorizontal TT.

It should be noted that the example partitioning split modes describedin Le Leannec and Li may be generally described as predefined splitmodes. More generally, according to the techniques described herein,partitioning a node according to a BT and TT split modes may includearbitrary BT and TT splitting. For example, referring to FIG. 10, theoffsets corresponding to a BT split (Offset₁) and a TT split (Offset₁and Offset₂) may be arbitrary instead of occurring at the predefinedlocations in Le Leannec and Li. There may be various techniques in whichto arbitrary offsets may be inferred and/or signaled. For example, fornodes having a size less than or equal to a threshold, a predefinedoffset may be inferred and for nodes of having a size greater than thethreshold, an arbitrary offset may be signaled.

In addition to BT and TT split types, T-shape split types may bedefined. FIG. 11 illustrates examples of T-shape partitioning. Asillustrated in FIG. 11, T-shape partitioning includes first partitioninga block according to a BT partition and further partitioning one of theresulting blocks according to the BT partition having a perpendicularorientation. As illustrated, a T-shape split results in three blocks. Inthe example illustrated in FIG. 11, the T-shape splits are described as2X T-shapes, where 2X T-shape partitioning may refer to a case where aT-shape partition is generated using two symmetric BT splits. Further,in FIG. 11, T-shape splits are defined based on which of the blocksresulting after the first partition is further partitioned (e.g., top orbottom for horizontal T-shapes and left or right for vertical T-shapes).Thus, the example T-shape split types in FIG. 11, may be described asbeing predefined. In a manner similar to that described above, withrespect to BT and TT split types, according to the techniques describedherein, partitioning a node according to a T-shape split modes mayinclude arbitrary T-shape splitting. It should be noted that in otherexamples, other partition modes may be defined, for example, a quadsplit about a single vertical or horizontal direction (e.g.,partitioning a square into four parallel equally sized rectangles). Asdescribed above, automatically partitioning fractional boundary videoblocks may adversely impact coding efficiency. Further, currenttechniques for partitioning fractional boundary video blocks may be lessthan ideal when various partition modes are available for partitioning anode.

FIG. 12 is a block diagram illustrating an example of a system that maybe configured to code (i.e., encode and/or decode) video data accordingto one or more techniques of this disclosure. System 100 represents anexample of a system that may perform video coding using partitioningtechniques described according to one or more techniques of thisdisclosure. As illustrated in FIG. 12, system 100 includes source device102, communications medium 110, and destination device 120. In theexample illustrated in FIG. 12, source device 102 may include any deviceconfigured to encode video data and transmit encoded video data tocommunications medium 110. Destination device 120 may include any deviceconfigured to receive encoded video data via communications medium 110and to decode encoded video data. Source device 102 and/or destinationdevice 120 may include computing devices equipped for wired and/orwireless communications and may include set top boxes, digital videorecorders, televisions, desktop, laptop, or tablet computers, gamingconsoles, mobile devices, including, for example, “smart” phones,cellular telephones, personal gaming devices, and medical imaginingdevices.

Communications medium 110 may include any combination of wireless andwired communication media, and/or storage devices. Communications medium110 may include coaxial cables, fiber optic cables, twisted pair cables,wireless transmitters and receivers, routers, switches, repeaters, basestations, or any other equipment that may be useful to facilitatecommunications between various devices and sites. Communications medium110 may include one or more networks. For example, communications medium110 may include a network configured to enable access to the World WideWeb, for example, the Internet. A network may operate according to acombination of one or more telecommunication protocols.Telecommunications protocols may include proprietary aspects and/or mayinclude standardized telecommunication protocols. Examples ofstandardized telecommunications protocols include Digital VideoBroadcasting (DVB) standards, Advanced Television Systems Committee(ATSC) standards, Integrated Services Digital Broadcasting (ISDB)standards, Data Over Cable Service Interface Specification (DOCSIS)standards, Global System Mobile Communications (GSM) standards, codedivision multiple access (CDMA) standards, 3rd Generation PartnershipProject (3GPP) standards, European Telecommunications StandardsInstitute (ETSI) standards, Internet Protocol (IP) standards, WirelessApplication Protocol (WAP) standards, and Institute of Electrical andElectronics Engineers (IEEE) standards.

Storage devices may include any type of device or storage medium capableof storing data. A storage medium may include a tangible ornon-transitory computer-readable media. A computer readable medium mayinclude optical discs, flash memory, magnetic memory, or any othersuitable digital storage media. In some examples, a memory device orportions thereof may be described as non-volatile memory and in otherexamples portions of memory devices may be described as volatile memory.Examples of volatile memories may include random access memories (RAM),dynamic random access memories (DRAM), and static random access memories(SRAM). Examples of non-volatile memories may include magnetic harddiscs, optical discs, floppy discs, flash memories, or forms ofelectrically programmable memories (EPROM) or electrically erasable andprogrammable (EEPROM) memories. Storage device(s) may include memorycards (e.g., a Secure Digital (SD) memory card), internal/external harddisk drives, and/or internal/external solid state drives. Data may bestored on a storage device according to a defined file format.

Referring again to FIG. 12, source device 102 includes video source 104,video encoder 106, and interface 108. Video source 104 may include anydevice configured to capture and/or store video data. For example, videosource 104 may include a video camera and a storage device operablycoupled thereto. Video encoder 106 may include any device configured toreceive video data and generate a compliant bitstream representing thevideo data. A compliant bitstream may refer to a bitstream that a videodecoder can receive and reproduce video data therefrom. Aspects of acompliant bitstream may be defined according to a video coding standard.When generating a compliant bitstream video encoder 106 may compressvideo data. Compression may be lossy (discernible or indiscernible) orlossless. Interface 108 may include any device configured to receive acompliant video bitstream and transmit and/or store the compliant videobitstream to a communications medium. Interface 108 may include anetwork interface card, such as an Ethernet card, and may include anoptical transceiver, a radio frequency transceiver, or any other type ofdevice that can send and/or receive information. Further, interface 108may include a computer system interface that may enable a compliantvideo bitstream to be stored on a storage device. For example, interface108 may include a chipset supporting Peripheral Component Interconnect(PCI) and Peripheral Component Interconnect Express (PCIe) busprotocols, proprietary bus protocols, Universal Serial Bus (USB)protocols, I²C, or any other logical and physical structure that may beused to interconnect peer devices.

Referring again to FIG. 12, destination device 120 includes interface122, video decoder 124, and display 126. Interface 122 may include anydevice configured to receive a compliant video bitstream from acommunications medium. Interface 108 may include a network interfacecard, such as an Ethernet card, and may include an optical transceiver,a radio frequency transceiver, or any other type of device that canreceive and/or send information. Further, interface 122 may include acomputer system interface enabling a compliant video bitstream to beretrieved from a storage device. For example, interface 122 may includea chipset supporting PCI and PCIe bus protocols, proprietary busprotocols, USB protocols, I²C, or any other logical and physicalstructure that may be used to interconnect peer devices. Video decoder124 may include any device configured to receive a compliant bitstreamand/or acceptable variations thereof and reproduce video data therefrom.Display 126 may include any device configured to display video data.Display 126 may comprise one of a variety of display devices such as aliquid crystal display (LCD), a plasma display, an organic lightemitting diode (OLED) display, or another type of display. Display 126may include a High Definition display or an Ultra High Definitiondisplay. It should be noted that although in the example illustrated inFIG. 12, video decoder 124 is described as outputting data to display126, video decoder 124 may be configured to output video data to varioustypes of devices and/or sub-components thereof. For example, videodecoder 124 may be configured to output video data to any communicationmedium, as described herein.

FIG. 13 is a block diagram illustrating an example of video encoder 200that may implement the techniques for encoding video data describedherein. It should be noted that although example video encoder 200 isillustrated as having distinct functional blocks, such an illustrationis for descriptive purposes and does not limit video encoder 200 and/orsub-components thereof to a particular hardware or softwarearchitecture. Functions of video encoder 200 may be realized using anycombination of hardware, firmware, and/or software implementations. Inone example, video encoder 200 may be configured to encode video dataaccording to the techniques described herein. Video encoder 200 mayperform intra prediction coding and inter prediction coding of pictureareas, and, as such, may be referred to as a hybrid video encoder. Inthe example illustrated in FIG. 13, video encoder 200 receives sourcevideo blocks. In some examples, source video blocks may include areas ofpicture that has been divided according to a coding structure. Forexample, source video data may include macroblocks, CTUs, CBs,sub-divisions thereof, and/or another equivalent coding unit. In someexamples, video encoder 200 may be configured to perform additionalsub-divisions of source video blocks. It should be noted that sometechniques described herein may be generally applicable to video coding,regardless of how source video data is partitioned prior to and/orduring encoding. In the example illustrated in FIG. 13, video encoder200 includes summer 202, transform coefficient generator 204,coefficient quantization unit 206, inverse quantization/transformprocessing unit 208, summer 210, intra prediction processing unit 212,inter prediction processing unit 214, filter unit 216, and entropyencoding unit 218.

As illustrated in FIG. 13, video encoder 200 receives source videoblocks and outputs a bitstream. As described above, current techniquesfor partitioning fractional boundary video blocks may be less thanideal. According to the techniques described herein, video encoder 200may be configured to apply a predefined partitioning to a fractionalboundary video block that minimizes the impact on coding efficiency.

In one example, according to the techniques described herein videoencoder 200 may be configured to apply a predefined partitioning to afractional boundary video block, where the predefined partitioning usesa combination of symmetric vertical and horizontal BT split modes togenerate CUs within the picture boundaries. That is, in one example,fractional boundary video block are partitioned using only symmetricvertical and horizontal BT split modes regardless of the partitioningmodes available for partitioning video blocks. FIG. 14A is a conceptualdiagram illustrating examples of predefined symmetric vertical andhorizontal BT split modes partitions for example fractional boundaryvideo blocks. FIG. 14B is a conceptual diagram illustrating an exampleof an inferred partitioning tree corresponding to the predefinedpartition illustrated in FIG. 14A. It should be noted that alternativeinferred partitioning trees may be used to generate the resultingpredefined partition of CTU₂. FIG. 14C illustrates an example of analternative inferred partitioning tree. It should be noted that in someexamples, the CUs illustrated in FIG. 14A within the picture boundaryresulting from the inferred partitioning may be further partitioned andin some examples, the CUs illustrated in FIG. 14A within the pictureboundary resulting from the inferred partitioning may not be furtherpartitioned. It should be noted that the example predefined partitionsillustrated in FIG. 14A result in fewer and larger corresponding CUswithin the picture boundary than the example predefined partitionsillustrated in FIG. 8.

In one example, according to the techniques described herein videoencoder 200 may be configured to apply a predefined partitioning to afractional boundary video block, where the predefined partitioning usesa combination of asymmetric vertical and horizontal BT split modes togenerate CUs within the picture boundaries. That is, in one example,fractional boundary video block are partitioned using only asymmetricvertical and horizontal BT split modes regardless of the partitioningmodes available for partitioning video blocks. In one example, theasymmetric vertical and horizontal BT split modes may include:horizontal partitioning at one quarter of the height (at the top for onemode or at the bottom for one mode) or vertical partitioning at onequarter of the width (at the left for one mode or the right for onemode). FIG. 15A is a conceptual diagram illustrating examples ofpredefined asymmetric vertical and horizontal BT split modes partitionsfor example fractional boundary video blocks. FIG. 15B is a conceptualdiagram illustrating an example of an inferred partitioning treecorresponding to the predefined partition illustrated in FIG. 15A. Itshould be noted that alternative inferred partitioning trees may be usedto generate the resulting predefined partition of CTU₂. FIG. 15Cillustrates an example of an alternative inferred partitioning tree. Itshould be noted that in some examples, the CUs illustrated in FIG. 15Awithin the picture boundary resulting from the inferred partitioning maybe further partitioned and in some examples, the CUs illustrated in FIG.15A within the picture boundary resulting from the inferred partitioningmay not be further partitioned. It should be noted that the examplepredefined partitions illustrated in FIG. 15A result in fewer and largercorresponding CUs within the picture boundary than the examplepredefined partitions illustrated in FIG. 8.

In one example, according to the techniques described herein videoencoder 200 may be configured to apply a predefined partitioning to afractional boundary video block, where the predefined partitioning usesa combination of vertical and horizontal TT split modes to generate CUswithin the picture boundaries. That is, in one example, fractionalboundary video block are partitioned using only asymmetric vertical andhorizontal TT split modes regardless of the partitioning modes availablefor partitioning video blocks. In one example, the vertical andhorizontal TT split modes may include: horizontal TT partitioning at onequarter of the height from the top edge and the bottom edge of a node;and vertical TT partitioning at one quarter of the width from the leftedge and the right edge of a node. FIG. 16A is a conceptual diagramillustrating examples of predefined asymmetric vertical and horizontalBT split modes partitions for example fractional boundary video blocks.FIG. 16B is a conceptual diagram illustrating an example of an inferredpartitioning tree corresponding to the predefined partition illustratedin FIG. 16A. It should be noted that alternative inferred partitioningtrees may be used to generate the resulting predefined partition ofCTU₂. FIG. 16C illustrates an example of an alternative inferredpartitioning tree. It should be noted that in some examples, the CUsillustrated in FIG. 16A within the picture boundary resulting from theinferred partitioning may be further partitioned and in some examples,the CUs illustrated in FIG. 16A within the picture boundary resultingfrom the inferred partitioning may not be further partitioned. It shouldbe noted that the example predefined partitions illustrated in FIG. 16Aresult in fewer and larger corresponding CUs within the picture boundarythan the example predefined partitions illustrated in FIG. 8.

As described above, in some cases, alternative inferred partitioningtrees may correspond to predefined partitions, for example, in the caseof CTU₂ in the examples above one or more inferred partitioning tressmay result in the same predefined partition. In one example, a set ofrules may be defined such that one of the inferred partitioning trees isselected. It should be noted that in some cases there may be practicalapplications for selecting a particular inferred partitioning tree oneinferred partitioning trees that result in the same partitioning. Forexample, in the following cases there may be practical applications forselecting a particular inferred partitioning tree: certain coding toolsmay only be available for certain partitioning types; the scan-order forcoding of the partitioning would be different, so the availability ofsamples and syntax information of previous/adjacent blocks would bedifferent, thereby effecting coding efficiency. Further, one inferredpartitioning tree may be selected as the partitioning tree with betterexpected coding efficiency.

It should be noted that with respect to the examples described abovewith respect to FIGS. 14A-16C, each of the examples may be generallydescribed as partitioning fractional boundary video block using a subsetof available partition modes. For example, with respect to the exampledescribed with respect to FIGS. 14A-14C, in one example, the followingpartitioning modes may be available: QT, and symmetric vertical andhorizontal BT split modes; with respect to the example described withrespect to FIGS. 15A-15C, in one example, the following partitioningmodes may be available: QT, symmetric vertical and horizontal BT splitmodes, and four additional asymmetric BT split modes; and with respectto the example described with respect to FIGS. 16A-16C, in one example,the following partitioning modes may be available: QT, symmetricvertical and horizontal BT split modes, and vertical and horizontal TTsplit modes. Thus, in one example, according to the techniques describedherein, fractional boundary video block may be partitioned using asubset of available partition modes and/or partition modes onlyavailable for partitioning fractional boundary video blocks (e.g., videoblocks that are not fractional boundary video blocks may be partitionedusing QTBT partitioning and fractional boundary video blocks may bepartitioned using TT partitioning).

In one example, the subset of available partition modes and/or partitionmodes only available for partitioning fractional boundary video blocksmay be based on one or more of the following: the distance of left-topsample (e.g., distance in terms of a number luma samples) of afractional boundary CTU from the right picture boundary; the distance ofleft-top sample of a fractional boundary CTU from the bottom pictureboundary; the resulting partitioning tree (and/or types of partitionsused in) of a spatially adjacent CTU; the resulting partitioning tree(and/or types of partitions used in) of a temporally adjacent CTU, wherea temporal adjacent CTU is co-located or offset by a motion vector; andallowed partitioning types for CTUs within a picture.

As described above, in some examples, CUs within the picture boundaryresulting from the inferred partitioning may be further partitioned. Inone example, according to the techniques described herein, CUs withinthe picture boundary resulting from the inferred partitioning may befurther partitioned using a subset of available partition modes and/orpartition modes only available for partitioning CUs within the pictureboundary resulting from the inferred partitioning. In one example, thesubset of available partition modes and/or partition modes onlyavailable for partitioning CUs within the picture boundary resultingfrom the inferred partitioning may be based on one or more of thefollowing: the distance of left-top sample of a CU from the rightpicture boundary; the distance of left-top sample of a CU from thebottom picture boundary; the distance of left-top sample of a CU fromthe right CTU boundary; the distance of left-top sample of a CU from thebottom CTU boundary; the resulting partitioning tree (and/or types ofpartitions used in) of a spatially adjacent CU; the resultingpartitioning tree (and/or types of partitions used in) of a temporallyadjacent CU, where a temporal adjacent CU is co-located or offset by amotion vector; and allowed partitioning types for CUs within a picture.Further, in one example the subset of available partition modes and/orpartition modes only available for partitioning CUs spanning a pictureboundary may be based on one or more of the following: the distance ofleft-top sample of a CU from the right picture boundary; the distance ofleft-top sample of a CU from the bottom picture boundary; the distanceof left-top sample of a CU from the right CTU boundary; the distance ofleft-top sample of a CU from the bottom CTU boundary; the resultingpartitioning tree (and/or types of partitions used in) of a spatiallyadjacent CU; the resulting partitioning tree (and/or types of partitionsused in) of a temporally adjacent CU, where a temporal adjacent CU isco-located or offset by a motion vector; and allowed partitioning typesfor CUs within a picture. In one example, an inferred partitioning maybe used when a block size exceeds a maximum TU size. Further, in oneexample, an inferred partitioning may be used when tile and/or sliceboundaries are not aligned with CTU boundaries.

In one example, an inferred partitioning may include determining toperform a QT partitioning in cases where all split edges resulting fromthe QT split lie outside of a picture boundary (e.g., a CTU extendsbeyond the bottom-right picture boundary). In one example, a QT splitmay be inferred if all its split edges resulting from the QT split lieoutside the picture boundary and the split edges are closest to thepicture boundary compared to another split, where closeness to a pictureboundary may be quantified according to the one or more of thefollowing: smallest vertical and horizontal distance, smallest verticaldistance, smallest horizontal distance, and/or smallest average ofhorizontal and vertical distance. In one example, an inferredpartitioning which includes determining to perform a QT partitioning mayfurther included determining a number of recursive QT splits to perform.The number of recursive QT splits to perform may be based on one or moreof the following parameters described above (e.g., the distance ofleft-top sample of a fractional boundary CTU from the right pictureboundary, slice type, etc.). It should be noted that in some examples,recursive QT splits may be conditionally applied to parent nodes. Forexample, if the minimum number of QT splits is equal to 2. A secondlevel QT split may be conditionally applied to each four nodes resultingfrom the first level split. For example, in one example, minimuminferred QT splits may be applicable only to nodes of that cross apicture boundary edge. In one example, if nodes resulting from a minimuminferred QT split cross picture boundary edge, another split type may beinferred from the node (e.g., BT horizontal) according to anycombination of the techniques described herein. For example, a needednumber of BT partitions may be determined for a node resulting from aminimum inferred QT split cross picture boundary edge according to thetechniques described below. Further, in one example, partitions that donot cause a split for block of samples inside picture boundary may beapplied according to the following:

if (bVerSplitAllowed && VertPartition != INFER_NONE && HorzPartition !=INFER_NONE && bVertPartitionInsidePicture==true)  {   bVerSplitAllowed =false;  }  if (bHorSplitAllowed && VertPartition != INFER_NONE && HorzPartition != INFER_NONE && bHorzPartitionInsidePicture==true)  {  bHorSplitAllowed = false;  } // != INFER_NONE implies that it is avalid option

Where,

-   -   bVerSplitAllowed indicates whether a binary vertical split is        allowed;    -   bHorSplitAllowed indicates whether a binary horizontal split is        allowed;    -   VertPartition !=INFER_NONE indicates a vertical partition is not        a valid option;    -   HorzPartition !=INFER_NONE indicates a horizontal partition is        not a valid option;    -   bHorzPartitionInsidePicture indicates whether a binary        horizontal split would cause a split for a block of samples        inside a picture boundary;    -   bVemPartitionInsidePicture indicates whether binary vertical        split for a block of samples inside a picture boundary.

In one example, at each implicit partitioning step, binary tree splitsin horizontal and vertical direction are chosen independently. For eachdirection the binary tree split that results in the split edge beingclosest to the picture boundary may be selected. Between the twocandidates (one for each direction) the one that does not partition theblock of samples inside the picture boundary is chosen, otherwise thehorizontal partition is chosen.

In one example, lower resolution pictures may use a larger minimumnumber of inferred QT splits compared to higher resolution pictures. Inone example, slices having an I-type (i.e., an I-slice) may use a largerminimum number of inferred QT splits compared to slices having a nonI-type. In one example, a luma channel of an I-slice may use a largerminimum number of inferred QT splits compared to a chroma channel of anI-slice. In one example, larger CTU sizes may use a larger number of aminimum number of inferred QT splits compared to smaller CTU sizes. Inone example, for CTUs spanning across picture boundary, when number ofsamples inside the picture boundary is relatively greater, then theminimum number of inferred QT splits is may be larger. In one example,when a QP value is relatively smaller, then the minimum number ofinferred QT splits is larger. In one example, the minimum number ofinferred QT splits may be larger, if adjacent blocks have a largernumber of QT splits.

As described above, in some cases, a CTU size may be 128×128 and apicture resolution may be 1920×1080. In such a case, the bottom row ofCTUs would include fractional boundary CTUs having 56 rows of sampleswith picture boundary. In similar manner, for a CTU size of 128×128 anda picture resolution 3840×2160, the bottom row of CTUs would includefractional boundary CTUs having 112 rows of samples with pictureboundary. Each of these cases, may occur relatively frequently and assuch in some cases, according to the techniques describe herein, defaultpartitioning may be defined for the bottom row CTUs. It should be notedthat in these cases, there may be several ways to partition a CTU suchthat one or more CUs are parallel to and included within the pictureboundary. In one example, according to the techniques herein, theresulting inferred partitions for these case are limited to power of twoblock sizes. In one case, the power of two block sizes are monotonicallydecreasing for blocks closer to the picture edge. In an example, thecoding order of blocks would be to code blocks further from the edgefirst.

In one example, for the case where a CTU size is 128×128 and a pictureresolution is 1920×1080, the bottom row CTUs may be partitioned suchthat the 56 rows of samples included within the picture boundary arepartitioned into a 128×48 upper CU and a 128×8 lower CU. In one example,the partitioning may be generated from a inferred tree illustrated inFIG. 17A.

In one example, for the case where a CTU size is 128×128 and a pictureresolution is 1920×1080, the bottom row CTUs may be partitioned suchthat the 56 rows of samples included within the picture boundary arepartitioned into a 128×32 upper CU, a 128×16 middle CU and a 128×8 lowerCU. In one example, the partitioning may be generated from a inferredtree illustrated in FIG. 17B. In one example, for the case where a CTUsize is 128×128 and a picture resolution is 1920×1080, the bottom rowCTUs may be partitioned such that the 56 rows of samples included withinthe picture boundary are partitioned into a 128×32 upper CU, a 128×8middle CU and a 128×16 lower CU. In one example, the partitioning may begenerated from a inferred tree illustrated in FIG. 17C. In one example,for the case where a CTU size is 128×128 and a picture resolution is1920×1080, the bottom row CTUs may be partitioned such that the 56 rowsof samples included within the picture boundary are partitioned into anupper 128×16 CU, a middle 128×32 CU, and a lower 128×8 CU. In oneexample, the partitioning may be generated from a inferred treeillustrated in FIG. 17D. It should be noted that in one example, each ofthe examples illustrated in FIGS. 17B, 17C, and 17D may be applied inthe cases where asymmetric BT partitioning is not allowed.

In one example, for the case where a CTU size is 128×128 and a pictureresolution is 3840×2160, the bottom row CTUs may be partitioned suchthat the 112 rows of samples included within the picture boundary arepartitioned into a 128×64 upper CU and a 128×48 lower CU. In oneexample, the partitioning may be generated from a inferred treeillustrated in FIG. 18A. In one example, for the case where a CTU sizeis 128×128 and a picture resolution is 3840×2160, the bottom row CTUsmay be partitioned such that the 112 rows of samples included within thepicture boundary are partitioned into a 128×96 upper CU and a 128×16lower CU. In one example, the partitioning may be generated from ainferred tree illustrated in FIG. 18B.

In one example, for the case where a CTU size is 128×128 and a pictureresolution is 3840×2160, the bottom row CTUs may be partitioned suchthat the 112 rows of samples included within the picture boundary arepartitioned into a 128×32 upper CU, a 128×64 middle CU, and a 128×16lower CU. In one example, the partitioning may be generated from ainferred tree illustrated in FIG. 18C. In one example, for the casewhere a CTU size is 128×128 and a picture resolution is 3840×2160, thebottom row CTUs may be partitioned such that the 112 rows of samplesincluded within the picture boundary are partitioned into a 128×64 upperCU, a 128×32 middle CU, and a 128×16 lower CU. In one example, thepartitioning may be generated from a inferred tree illustrated in FIG.18D. It should be noted that in one example, each of the examplesillustrated in FIGS. 18C and 18D may be applied in the cases whereasymmetric BT partitioning is not allowed.

It should be noted that in some cases, a tile or slice may include onlyfractional boundary CTU's. In such cases, the techniques describedabove, may be used for partition the fractional boundary CTU's includedin the slice or tile.

As described above, JEM includes the parameters MinQTSize, MaxBTSize,MaxBTDepth, and MinBTSize for use in signaling of a QTBT tree. It shouldbe noted that with respect MinQTSize and MaxBTSize there may be variousways in which a size may be specified. In one example, size may bespecified according to a threshold dimension value and, in the case ofMaxBTSize, if either the height or the width exceeds the dimension valuethe block is not allowed to be split according to a BT split mode. Insome cases, a predefined partitioning for a fractional boundary videoblock may be inconsistent with values of MinQTSize, MaxBTSize,MaxBTDepth, and MinBTSize. For example, referring to block CTU₂, in theexample illustrated in FIG. 14A, as illustrated in FIG. 14B, a verticalBT split occurring at BT depth 3 is used to generate the right-most CUincluded within the picture boundary. In this case, when fractionalboundary video block are partitioned using only symmetric vertical andhorizontal BT split modes, the partitioning of CTU₂ illustrated in FIG.14A, would be inconsistent with MaxBTDepth being less than 3. Further,in the case where the CTU is 128×128, in order for the partitioning ofCTU₂ illustrated in FIG. 14A, to be consistent with MaxBTSize would berequired to be greater than or equal to 128 (e.g., when MaxBTSize isexpressed as a dimension threshold value). In one example, in order toensure compliance with values of MinQTSize, MaxBTSize, MaxBTDepth,and/or MinBTSize, video encoder 200 may be configured to applyexceptions to a predefined partitioning for fractional boundary videoblocks. For instance, in one example, video encoder 200 may beconfigured to enable additional available partition modes other than thetypes used according to a predefined partitioning. For example, withrespect to the example of CTU₂ illustrated in FIG. 14A, video encoder200 may be configured to enable QT partitioning when MaxBTDepth is setto a value less than 3. FIG. 20 illustrates an example where QTpartitioning is enabled for partitioning CTU₂. In one example, the QTpartitioning may be enabled for partitioning CTU₂, until constraintscorresponding to set values of MaxBTSize, MaxBTDepth, and/or MinBTSizecan be satisfied. In one example, the QT partitioning may be enabled forpartitioning CTU₂ without restriction. In a similar manner, asymmetricBT partitioning may be used for partitioning fractional boundary videoblocks, even if the use of asymmetric BT partitioning is not allowed forother CTU's. It should be noted that in some cases, the use ofasymmetric BT partitioning for partitioning fractional boundary videoblocks may be restricted until constraints corresponding to set valuesof MaxBTSize, MaxBTDepth, and/or MinBTSize can be satisfied. It shouldbe noted that in some examples, an exception may include enablingpartitioning types for fractional video blocks that are disabled basedon a video layer property (e.g., allow an exception to disablingasymmetric BT partitionings for higher temporal layers). Further, insome examples, splits may be inferred based on temporal layer values.For example, one or more aspects of a QT inference may be disabled forhigher temporal layers. Further, in some cases, explicit signaling maybe used to indicate whether QT inference is disabled for a temporallayer (e.g., a flag may be signaled for each respective layer). In somecases, one or more inference rules may be defined to determine whetherQT inference is disabled for a temporal layer. For example, a temporallayer threshold value at which QT inference is disabled may bedetermined based on coding parameters and/or video properties. Further,in some examples a temporal layer threshold value may be signaled.Further, in some examples MaxBTDepth may be incremented or decrementedbased on a temporal layer value. In a similar manner, a QP value may bedetermined for a slice or a picture and splits may be inferred based onthe determined QP value.

Further, in some examples, values of MinQTSize, MaxBTSize, MaxBTDepth,and/or MinBTSize may be set differently, not applied, or changed forfractional boundary video blocks (i.e., set values may be overridden).For example, one or more of the following may be applied for fractionalboundary video blocks: increase the value of MaxBTSize for fractionalboundary video blocks; and/or increase the value of MaxBTDepth forfractional boundary video blocks. In one example, MaxBTSize may be setfor fractional boundary video blocks based on one or more of: a slicetype; a value of MaxBTSize for non-fractional boundary video blocks;and/or a maximum, an average, a median, and/or a minimum size of BTnodes resulting from the partitioning of a subset of CTUs in one or morepreviously coded pictures. For example, for a non-boundary CTU in apreviously coded picture, the size of the smallest resulting BT node maybe 32×64. Based on this value, the MaxBTSize may be set for fractionalboundary video blocks as, for example, 128. In one example, whenMaxBTSize is set as threshold dimension which is applied to both aheight and width dimension, MaxBTSize, may be set such that its value isgreater than or equal to the maximum of the smallest resulting BT node(e.g., MaxBTSize>=max(height, width), where max(x,y) returns x, if x isgreater than or equal to y, otherwise returns y). In one example, whenMaxBTSize is set as threshold dimension that is set respectively foreach of height and width dimension (e.g., MaxBTSizeH for height andMaxBTSizeW for width), MaxBTSize may be set such that each respectivevalue is greater than or equal to the corresponding value of thesmallest resulting BT node (e.g., MaxBTSizeH >=height andMaxBTSizeW>=width). In some examples, values of MinQTSize, MaxBTSize,MaxBTDepth, and/or MinBTSize may be set differently, not applied, orchanged for fractional boundary video blocks by signaling values in abitstream, for example, in parameter sets, slice headers, video blocksignaling etc.

Further, in some examples, for inter slices MaxBTSize may be set to apredetermined value (e.g., CTU size) for fractional boundary videoblocks. In one example, MaxBTDepth may be set for fractional boundaryvideo blocks based on one or more of: a slice type; and/or the boundaryedge type (i.e., right, bottom, or bottom-right) that the fractionalboundary video block intersects. In one example, MaxBTDepth may beincreased based on a predefined value, and/or a value that enables adesired partitioning. Further, in some examples, MaxBTDepth may befurther increased according to a safety margin value. In one example,MaxBTDepth may be increased based on a depth at which a final BT splitoccurs to generate a particular partition, where the final BT split is aBT split at the lowest level in a BT split hierarchy for the particularpartition. For example, referring to block CTU₂, in the exampleillustrated in FIG. 14A, the depth at which the final BT split occurs togenerate the right-most CU included within the picture boundary, i.e., 3may be added to a current value of MaxBTDepth to increase the MaxBTDepthfor a fractional boundary video block. Examples of techniques fordetermining a depth required to generate a particular partition aredescribed in further detail below. It should be noted that a currentvalue of MaxBTDepth may be derived from spatial-temporal adjacent blocks(e.g., CUs, CTUs, PUs, TUs, etc.) and/or from higher level signaling(e.g. parameter sets and/or a slice header). Further, in some examples,MaxBTDepth may be increased based on the number of BT splits needed (orused) to generate a particular partition (i.e., a BT split count value).For example, referring to block CTU₂, in the example illustrated inFIGS. 14A and 14B, the BT split count value required be to generate theright-most CU included within the picture boundary is 4. This value maybe added to a current value of MaxBTDepth to increase the MaxBTDepth fora fractional boundary video block. In one example, a BT split countvalue may correspond to the largest number of BT splits that need to betraversed from the root (i.e., CTU-level) in a partition tree to reach aCU in a particular partitioning.

As described above, with respect to FIG. 17A, for the case where a CTUsize is 128×128 and a picture resolution is 1920×1080, the bottom rowCTUs may be partitioned such that the bottom row CTUs may be partitionedsuch that the 56 rows of samples included within the picture boundaryare partitioned into a 128×48 upper CU and a 128×8 lower CU. Asillustrated in FIG. 17A, the BT split count value to generate the 128×8lower CU included within the picture boundary is 3 and the depth atwhich the final BT split occurs is 2. As described above, with respectto FIG. 18B, for the case where a CTU size is 128×128 and a pictureresolution is 3840×2160, the bottom row CTUs may be partitioned suchthat the 112 rows of samples included within the picture boundary arepartitioned into a 128×96 upper CU and a 128×16 lower CU included withinthe picture boundary. As illustrated in FIG. 18B, the BT split countvalue to generate the 128×16 lower CU included within the pictureboundary is 3 and the depth at which the final BT split occurs is 2. Inone example, in these cases, a new value for MaxBTDepth may bedetermined for fractional boundary video blocks by using one or more ofthe following techniques: adding a predefined value to MaxBTDepth,adding a predefined value to MaxBTDepth and a safety margin value toMaxBTDepth, and/or setting MaxBTDepth, wherein the technique used and/ora predefined value is determined based on the CTU size and/or picturesize. More generally, a particular combination of CTU size and picturesize may be associated with a particular predefined partitioning forfractional boundary video blocks, where the predefined partitioning isassociated with a BT split count value and a depth value at which thefinal BT split occurs. The BT split count value and/or the depth valueat which the final BT split occurs for the predefined partitioning maybe used to modify MaxBTDepth.

As described above, having a relatively large number of relatively smallvideo blocks occurring at or near a picture boundary may adverselyimpact coding efficiency. More generally, how a fractional video blockis partitioned impacts coding efficiency. For example, referring to FIG.21, there may be several ways to partition a fractional video blockhaving a height, curH, and a width, curW, such that height, blkH, andwidth, blkW, are included within the picture boundary. It should benoted that in this general case, curH and curW may be less than or equalto a CTU size. That is, the fractional video block may be a CTU or asmaller video block. Further, as described above, MaxBTDepth may beincreased for fractional video blocks. When MaxBTDepth is increased, alarger set of possible partitionings become available for partitioning aCTU. Increasing the set of possible partitionings available forpartitioning a CTU can, in some cases, slow down a video encoder (i.e.,decrease video encoder performance). For example, a video encoderimplementation that evaluates all (or a significant portion) of thepossible partitionings when selecting a particular partitioning for aCTU may see a decrease in performance as MaxBTDepth is increased, asthere are more possible partitionings to evaluate. According to thetechniques described herein, video encoder 200 may be configured topartition a fractional video block based on curH, curW, blkH, and blkWand the available BT split modes in a manner that increases codingefficiency. Further, video encoder 200 may be configured to increaseMaxBTDepth for fractional video blocks in a manner that mitigates apotential decreases in video encoder performance.

In one example, video encoder 200 may be configured to determine a valueindicating a needed number of BT partitions, or splits, (e.g., a BTsplit count value, N_BT_Part) in order for the portion of the fractionalvideo block corresponding to blkH and blkW to be included within thepicture boundary. In some examples, the needed number of BT partitionsmay be used to partition a video block and/or increase MaxBTDepth. Itshould be noted that while a needed number of partitions is inherentlybased on curH, curW, blkH, and blkW and the available BT split modes,the needed number of partitions may also be based on a slice type.Further, it should be noted that there may be various processes fordetermining the needed number of partitions based on curH, curW, blkH,and blkW and the available BT split modes, where some processes are moreefficient than others. According to the techniques described herein,video encoder 200 and video decoder 300 may be configured to determine aneeded number of partitions based on the algorithm described below. Itshould be noted that with respect to the algorithm described below, theavailable BT split modes for a fractional video block include symmetricvertical and horizontal BT split modes, and the four additionalasymmetric BT split modes described above.

Video encoder 200 and video decoder 300 may be configured to determine aneeded number of partitions based on the following algorithm:

-   -   Determine values mults3CountH and mults3CountW, where        mults3CountH indicates N of 3^(N) in the prime factorization of        blkH and mults3CountW indicates N of 3^(N) in the prime        factorization of blkW;    -   Set variable neededBTPartitions to 0;    -   Until a horizontal partition is aligned with picture boundary:        -   Select a horizontal BT split mode according to a set of            partitioning rules, where Hor_Down may only be selected if            mults3CountH>0.            -   For each selection of Hor_Down, reduce mults3CountH by                1;            -   For each selected horizontal BT split mode, increment                neededBTPartitions by 1;            -   For each selected Horizontal BT split mode, update                cures, blkH, and mults3CountH for the current video                block that spans across (or touches) the horizontal                picture boundary;    -   Until a vertical partition is aligned with picture boundary:        -   Select a vertical BT split mode according to a set of            partitioning rules, where Ver_Right may only be selected if            mults3CountV>0.            -   For each selection of Ver_Right, reduce mults3CountV by                1;            -   For each selected vertical BT split mode, increment                neededBTPartitions by 1;            -   For each selected Vertical BT split mode, update curW,                blkW, and mults3CountW for the current video block that                spans across (or touches) the vertical picture boundary;    -   Output neededBTPartitions

It should be noted that in the example algorithm above, the order inwhich the horizontal partitioning and the vertical partitioning areperformed may be interchanged. Further, individual horizontalpartitioning and vertical partitioning steps may be performed accordingto a defined order. For example, horizontal partitioning and thevertical partitioning may be performed by alternating the performance ofhorizontal and vertical partitionings. In one example, horizontalpartitioning and the vertical partitioning may be performed byalternating the performance of a set number of horizontal and verticalpartitionings (e.g., perform two horizonal, then two vertical, then twohorizontal, etc.). In one example, selection preference may be given toone of horizontal or vertical BT partition modes. For example,horizontal BT partition modes may be executed until one of thepartitioning edges aligns with the horizontal picture boundary, beforeperforming any vertical BT partition modes. As provided in the examplealgorithm above, BT split modes are selected according to a set ofpartitioning rules. That is, a set of partitioning rules includes rulesfor selecting one of: a symmetric BT mode, a one-quarter asymmetric BTsplit mode (i.e., Hor_Up and Ver_Left), or a three-quarter asymmetric BTsplit mode (i.e., Hor_Down and Ver_Right). In one example, a predefinedrule may include selecting one of a symmetric BT mode, a one-quarterasymmetric BT split mode, or a three-quarter asymmetric BT split modethat provides the greatest reduction of curH (or curV) and/or blkH (orblkW) when updated. For example, if curH is equal to 128 and blkH isequal to 112, after a symmetric BT split, curH would be equal to 64 andblkH would be equal to 48, after a Hor_Up split, curH would be equal to96 and blkH would be equal to 80, and after a Hor_Down split, curH wouldbe equal to 32 and blkH would be equal to 16. In this case, the Hor_Downsplit provides the greatest reduction in curH and blkH. However, in thiscase, mults3CountH is not greater than 0. Thus, in this case, in oneexample, a symmetric BT split may be selected as it provides a greaterreduction in curH and blkH than Hor_Up. In one example, a predefinedrule may include selecting one of a symmetric BT mode, a one-quarterasymmetric BT split mode, or a three-quarter asymmetric BT split modebased which partition mode results in partition boundary which is theclosest to a picture boundary. For example, FIG. 22 illustrates anexample of respective possible horizontal boundaries resulting from eachof a symmetric BT mode, a one-quarter asymmetric BT split mode, or athree-quarter asymmetric BT split mode in relation to a horizontalpicture boundary. As illustrated in FIG. 22, the boundary resulting fromthe symmetric BT mode is the closest to a picture boundary. Thecloseness of a boundary to the picture boundary may be quantifiedaccording to an absolute distance value. For example, in the exampleillustrated in FIG. 22, in the case where curH is 128 and blkH is 56,for the symmetric BT mode, the resulting partition corresponds to curHequal to 64, blkH equal to 56, and a distance between the partitionboundary and the picture boundary of 8; for the one-quarter asymmetricBT split mode, the resulting partition corresponds to a curH equal to32, blkH equal to 24, and a distance between the partition boundary andthe picture boundary of 24; and for the three-quarter asymmetric BTsplit mode, the resulting partition corresponds to curH equal to 96,blkH equal to 54, and a distance between the partition boundary and thepicture boundary of 40.

It should be noted in cases where a selection is based on the greatestreduction of one of currH (or currV), blkH (or blkW), and/or a distancevalue, and two partition modes provide the same reduction and/ordistance value, the partition mode that provides the least number ofpartitionings inside the picture is selected and/or a default order ofpartitioning modes may be used as a tie-breaker. In one example,selection preference may be given to symmetric BT partition modes. Forexample, horizontal symmetric BT partitions may be executed until one ofthe partitioning edges aligns with the horizontal picture boundary. Ingeneral, selection preference may be given to a BT partitioning thatintroduces the fewest number of partitioning inside the picture.

In one example, a predefined rule may include selecting one of asymmetric BT mode or a TT split mode based on which partition moderesults in partition boundary which is the closest to a pictureboundary. For example, FIG. 23 illustrates an example of respectivepossible horizontal boundaries resulting from each of a symmetric BTmode or TT split mode and FIG. 24 illustrates an example of respectivepossible vertical boundaries resulting from each of a symmetric BT modeor TT split mode. As illustrated in FIG. 23 and FIG. 24, distances a, b,and c represent the distance between a boundary resulting from a splitand the picture boundary. With respect to FIG. 23, closeness may bedetermined as follows: if(min(abs(a), abs(c))<abs(b)), then select TThorizontal partition; otherwise, select BT horizontal partition.Similarly, with respect to FIG. 24, closeness may be determined asfollows if(min(abs(a), abs(c))<abs(b)), then select TT verticalpartition; otherwise, select BT vertical partition. It should be notedthat in one example, in cases where a fractional video block intersectsa vertical and a horizontal picture boundary, in one example, horizontalpartitioning that includes selection of a symmetric BT mode or a TTsplit mode as described above may be performed, then verticalpartitioning that includes selection of a symmetric BT mode or a TTsplit mode may be performed.

In some cases, a partition type is selected for a fractional video blockonly if at least one of the split partitionings aligns with a pictureboundary (i.e., the resulting distance is 0). For example, a TT splitmode is only selected if at least one of the split partitionings alignswith a picture boundary.

As described above, there may be common cases generating fractionalvideo blocks based on combination of a CTU size and a picture size(e.g., a CTU size is 128×128 and a picture size is 1920×1080 or a CTUsize is 128×128 and a picture size is 3840×2160). In some examples, aset of partitioning rules may be defined for a CTU size and a picturesize combination. That is, in general, a particular combination of CTUsize and picture size may be associated with a particular predefinedpartitioning for fractional boundary CTUs. For example, for the casewhere a CTU size is 128×128 and a picture size is 1920×1080 or3840×2160, a set of partitioning rules may include the following:

 if ((curH==128 && blkH==112) ∥ (curH==64 &&  blkH==56))   {   selectedMode = infer HOR_Down;   }   else if (curH==128 && blkH==56)  {    selectedMode = infer Horizontal BT;   } and  if ((curW==128 &&blkW==112) ∥ (curW==64 &&  blkW==56))   {    selectedMode = inferVER_Right;   }   else if (curW==128 && blkW==56)   {    selectedMode =infer Vertical BT;   }

where,

-   -   == is the equal to relational operator;    -   x&&y is the Boolean logical “and” of x and y;    -   x∥y is the Boolean logical or of x and y.

It should be noted that, in some examples, the example partitioningrules above may be applied independent of picture size. Further, itshould be noted that a set of partitioning rules may include acombination of rules, where, for example, the combination of rules arebased on video and/or coding properties.

It should be noted that in the example algorithm above, a three-quarterasymmetric BT split mode are not allowed to be selected unlessrespective values of mults3CountH and mults3CountV are greater than 0.If this constraint was not in place, there may be cases where athree-quarter asymmetric BT split results in a block dimension not beinga power of 2. For example, if a 32×32 block is split using Vert_Right,the resulting blocks are 24×32 and 8×32 (24 is not a power of 2). Havinga block that is not a power of 2 may influence subsequent steps increating a partitioning and may lead to a partitioning with an excessivenumber of partitionings. Therefore, in some cases, a three-quarterasymmetric BT split mode is only allowed to be selected, if a multipleof 3 exists in the prime factorization of block size/dimension beingconsidered. Further, it should be noted that in some examples, luma andchroma channels of a fractional video block may share a partitioning(e.g., a partitioning provided according to the algorithm above). Insome examples, luma and chroma channels of a fractional video block mayuse different partitionings (e.g., for I-slices, the algorithm above maybe applied independently to each channel).

As described above, when MaxBTDepth is increased, the correspondingincrease in the set of possible partitionings may decrease video encoderperformance. In one example, in order to mitigate a decrease in videoencoder performance, a height threshold may be determined as thesmallest height block inside a picture when only QT partitioning is usedto create a partitioning tree and a width threshold may be determined asthe smallest height block inside picture when only QT partitioning isused to create a partitioning. For example, referring to FIG. 8, if CTU₂is 128×128, the height threshold would be 32 and the width thresholdwould be 32. Based on the height threshold and the width threshold,partitioning of a fractional video block according to a subset ofavailable partitioning modes (e.g., symmetric BT and asymmetric BT) maybe performed until a condition based on the height threshold and/orwidth threshold is satisfied. For example, in one example, during thehorizontal partitioning of a video block, if the current height of blockexceeds the height threshold, then only horizontal symmetric BTpartitioning is allowed. It should be noted that this condition does notlimit vertical partitioning types. Further, in one example, during thevertical partitioning of a video block, if the current width of a blockexceeds the width threshold, then only vertical symmetric BTpartitioning is allowed. It should be noted that this condition does notlimit horizontal partitioning types. It should be noted that in someexamples, a common threshold value may be defined, (e.g., a maximumdimension of block). Further, it should be noted that the split mode ofnot splitting the block may be available. It should be noted thatlimiting partitioning types that may be selected based on a thresholdvalue may be used to modify signaling, such that the signaling onlyindicates partition types that may be selected (e.g., partition typeindexing may be simplified based on a reduced number of partitioningtypes that may be selected). Such signaling modifications may result inimproved coding efficiency. It should be noted that in some examples,instead of height and width thresholds, a threshold may be defined as anumber of samples of a video block (e.g., 1,024). Further, it should benoted that thresholds may be further based on other video and videocoding properties. For example, the threshold may be increased ordecreased from a determined value based on slice type. Further, in oneexample, different thresholds may be set for different regions of a CTU.For example, a upper portion of a CTU may have an increased threshold.

It should be noted that in some cases, a partition mode may result in ablock size that is not supported (e.g., not supported for a subsequentvideo coding process). In one example, a partitioning type resulting inthat block size that is not supported may be disallowed. In one example,an exception may be made for a fractional video block and thepartitioning type may be used although it would otherwise result in ablock size that is not supported. It should be noted that in this case,in some examples, a subsequent video coding process may be modified tohandle such an exception.

As described above, a video encoder may evaluate possible partitioningsfrom set of possible partitionings. In one example, according to thetechniques herein, video encoder 200 may be configured to identify allvalid partitions of a fractional video block, according to theconstraints described above (e.g., allowed partition types, BT depthconstraints, etc.), where a valid partitioning may be defined as apartitioning that results in no leaves of the partitioning tree spanningacross picture boundary without further partitioning once this conditionis satisfied. It should be noted that subsequent further partitioning ofa valid partitioning may be allowed. Video encoder 200 may label eachvalid partition with an index value. It should be noted that indexingmay correspond to a defined order in which valid partitionings aregenerated. For example, the algorithm above may determine validpartitions based on a defined preference order of partition typeselection. Video encoder 200 may then select one of the valid partitions(e.g., based on a rate-distortion optimization algorithm). Video encoder200 may signal the selected partition using the index value. In thismanner, a video decoder may perform the same process as video encoder toidentify and index the valid partitions and determine the selectedpartition by parsing an index value from a bitstream. It should be notedthat a process of identifying and indexing valid partitions may beshared or performed independently for luma and chroma channels.

As described above with respect to FIG. 10, in some examples, theoffsets corresponding to a BT split (Offset₁) may be arbitrary insteadof occurring at the predefined locations. In one example, according tothe techniques herein, video encoder 200 may be configured to usearbitrary offset partitioning for fractional video blocks. For example,non-fractional video blocks may be partitioned according to a basepartitioning technique (e.g., QTBT partitioning) with correspondingsyntax and semantics and fractional video blocks may be partitionedaccording to an arbitrary offset partitioning technique withcorresponding syntax and semantics. For example, for fractional videoblocks offset values such as, 56 and 112 may be signaled as used forpartitioning. It should be noted that an arbitrary offset partitioningtechnique may include signaling a horizontal offset value and a verticaloffset value. For example, referring to FIG. 21 respective offset valuesmay be signaled for blkH and blkW. Further, it should be noted that insome examples, offset values may be inferred. For example, forparticular combinations of a CTU size and a picture size, an offsetvalue may be inferred for partitioning fractional boundary CTUs. Forexample, in the case of a CTU size of 128×128 and a picture size of1920×1080, in one example, if a one-quarter asymmetric horizontal BTsplit mode (or a symmetric horizontal BT split mode or a three-quarterasymmetric horizontal BT split mode) is signaled at the root of afractional boundary CTU (according to syntax and semantics used forpartitioning non-fraction CTUs), the signaled split may be inferred ascorresponding to an asymmetric horizontal BT split mode having an offsetof 56. It should be noted that in some examples, further partitioningmay be enabled for the block resulting from the arbitrary offsetpartitioning.

As described above, a fractional boundary video block may be partitionedusing a subset of available partition modes. In one example, videoencoder may be configured to signal a partition for a fraction boundaryvideo block a according to a subset of available partitioning modes. Inone example, the option of not splitting a fraction boundary video blockmay be disallowed. In such an example, the binarization used to signal anon-fractional boundary video block may be modified for signaling thepartitioning of a fraction boundary video block. For example, in a casewhere a non-fractional boundary video block may be partitioned using acombination of the QT partitioning, symmetric BT partitioning, ABTpartitioning, and TT partitioning according to the example of bin codingsignaling illustrate in Table 1. In one example, in the case where theoption of not splitting a fraction boundary video block is disallowed,the example bin coding signaling illustrated in Table 2 may be used tosignal a partitioning for a fraction boundary video block. In oneexample, in the case where the option of not splitting a fractionboundary video block is disallowed, the example bin coding signaling mayinclude a Bin₀ indicating a QT split or a symmetric BT and Bin₁indicating a BT split direction (e.g., 0=QT; 10=Horizontal BT; and11=Vertical BT), until the fraction boundary video block is partitionedto a point where no further splitting is allowed.

TABLE 1 Bin Coding Bin₀ Bin₁ Bin₂ Bin₃ Bin₄ Bin₅ Partition Type 1 N/AN/A N/A N/A N/A Quad 0 0 N/A N/A N/A N/A Leaf Node 0 1 0 0 N/A N/AHorizontal Triple Tree at ¼ of block dimension. (Horizontal TT) 0 1 1 0N/A N/A Vertical Triple Tree at ¼ of block dimension. (Vertical TT) 0 10 1 0 N/A Horizontal BT 0 1 0 1 1 0 Horizontal ABT at ¼ from top(Hor_Up) 0 1 0 1 1 1 Horizontal ABT at ¼ from bottom (Hor_Down) 0 1 1 10 N/A Vertical BT 0 1 1 1 1 0 Vertical ABT at ¼ from left (Ver_Left) 0 11 1 1 1 Vertical ABT at ¼ from right (Ver_Right)

TABLE 2 Bin Coding Bin₀ Bin₁ Bin₂ Bin₃ Bin₄ Partition Type 0 N/A N/A N/AN/A Quad 1 0 1 N/A N/A Horizontal Triple Tree at ¼ of block dimension.(Horizontal TT) 1 1 1 N/A N/A Vertical Triple Tree at ¼ of blockdimension. (Vertical TT) 1 0 0 0 N/A Horizontal BT 1 0 0 1 1 HorizontalABT at ¼ from top (Hor_Up) 1 0 0 1 0 Horizontal ABT at ¼ from bottom(Hor_Down) 1 1 0 0 N/A Vertical BT 1 1 0 1 1 Vertical ABT at ¼ from left(Ver_Left) 1 1 0 1 0 Vertical ABT at ¼ from right (Ver_Right)

In one example, if the portion of a fractional boundary video blockextended within the picture boundary matches (e.g., same width, height)a supported size of a coding structure (e.g., a transform unit,prediction unit, or coding unit) then the supported size is used forcoding the block extent inside the picture boundary. That is, thefractional boundary video block is partitioned to the correspondingsupport size. In one example, such a determination may be made by avideo decoder when a corresponding partitioning signal is received forthe fractional boundary video block (e.g., if NO_SPLIT is received,partition to supported size). In one example, a video decoder maypartition the fractional boundary video to a supported size using aninference rule (i.e., without receiving explicit signaling).

As described above, an inferred partitioning of a fractional video blockmay include performing a number of recursive QT splits. In one example,the number of recursive QT splits to perform may be indication accordingSPS, PPS, and/or slice header signaling. In one example the signalingmay be based on the following semantics:

Sequence parameter set { ... sps_min_QT_split_for_CTU_at_right_picture_edge sps_min_QT_split_for_CTU_at_bottom_picture_edge sps_min_QT_split_for_CTU_at_rightbottom_picture_corner sps_slice_level_override_present ... } Slice header { ...  if(sps_slice_level_override_present)  {  slice_min_QT_split_for_CTU_at_right_picture_edge  slice_min_QT_split_for_CTU_at_bottom_picture_edge  slice_min_QT_split_for_CTU_at_rightbottom_picture_corner  } ... }

Where each of the example syntax elements X_min_QT_split_for_CTU_at_Yindicate the minimum number of QT splits to be performed for acorresponding CTU, and

-   -   sps_slice_level_override_present indicates the presence of a        slice level value that overrides the SPS level values.

It should be noted that in one example, a slice header may alsoadditionally include a presence flag. In this manner, only selectedslices (i.e., according to the value of the slice header presence flag)override the SPS level signaling. In particular, in one example,signaling may be based on the following semantics:

Sequence parameter set { ... sps_min_QT_split_for_CTU_at_right_picture_edge sps_min_QT_split_for_CTU_at_bottom_picture_edge sps_min_QT_split_for_CTU_at_rightbottom_picture_corner sps_slice_level_override_present ... } Slice header { ...  if(sps_slice_level_override_present)  {  slice_level_override_flag if(slice_level_override_flag)   {  slice_min_QT_split_for_CTU_at_right_picture_edge  slice_min_QT_split_for_CTU_at_bottom_picture_edge  slice_min_QT_split_for_CTU_at_rightbottom_picture_corner   }  } ... }

Where slice_level_override_flag indicates the presence of subsequentsyntax elements as illustrated.

In one example, the signaling may be based on the following semantics,which may be included, for example, in one of a parameter set or a sliceheader:

{ ...  same_min_QT_split_value_for_all_boundary_CTUs_flag  if(same_min_QT_split_value_for_all_boundary_CTUs_flag)  {  min_QT_split_for_CTU_at_boundary  }  else  { min_QT_split_for_CTU_at_right_picture_edge min_QT_split_for_CTU_at_bottom_picture_edge min_QT_split_for_CTU_at_rightbottom_picture_corner  } ... }

Where same_min_QT_split_value_for_all_boundary_CTUs_flag indicated thesame number of splits as provided by min_QT_split_for_CTU_at_boundary isapplied to all of the fraction boundary CTUs.

In one example, when same_min_QT_split_value_for_all_boundary_CTUs_flagis not present in a bitstream (e.g. implicit signaling) it is inferredto a default value (e.g., 1).

In one example, the signaling may be based on the following semantics:

Sequence parameter set { ... min_QT_split_for_CTU_edge_signaled if(min_QT_split_for_CTU_edge_signaled){ same_min_QT_split_value_for_all_boundary_CTUs_flag   if(same_min_QT_split_value_for_all_boundary_CTUs_flag)   {  min_QT_split_for_CTU_at_boundary   }   else   {  min_QT_split_for_CTU_at_right_picture_edge  min_QT_split_for_CTU_at_bottom_picture_edge  min_QT_split_for_CTU_at_rightbottom_picture_corner   } sps_slice_level_override_present  }

Slice header { ...  if (sps_slice_level_override_present)  { slice_level_override_flag  if(slice_level_override_flag)   if(same_min_QT_split_value_for_all_boundary_CTUs_flag)   {  slice_min_QT_split_for_CTU_at_boundary   }   else   {  slice_min_QT_split_for_CTU_at_right_picture_edge  slice_min_QT_split_for_CTU_at_bottom_picture_edge  slice_min_QT_split_for_CTU_at_rightbottom_picture_corner   }  } ... }

Where min_QT_spli_for_CTU_edge_signaled indicates the presence ofsubsequent syntax elements as illustrated.

It should be noted that in some cases,min_QT_split_for_CTU_edge_signaled may not be present in a bitstream(e.g. implicit signaling) and may be inferred to a default value 0 or1).

In one example, the signaling may be based on the following semantics:

Sequence parameter set { ... min_QT_split_for_CTU_edge_signaled if(min_QT_split_for_CTU_edge_signaled) { same_min_QT_split_value_for_all_boundary_CTUs_flag   if(same_min_QT_split_value_for_all_boundary_CTUs_flag)   {  min_QT_split_for_CTU_at_boundary   }   else   {  min_QT_split_for_CTU_at_right_picture_edge  min_QT_split_for_CTU_at_bottom_picture_edge  min_QT_split_for_CTU_at_rightbottom_picture_corner   } sps_slice_level_override_present  } Slice header { ...  if(sps_slice_level_override_present)  {  slice_level_override_flag if(slice_level_override_flag)   {  slice_min_QT_split_for_CTU_at_right_picture_edge  slice_min_QT_split_for_CTU_at_bottom_picture_edge  slice_min_QT_split_for_CTU_at_rightbottom_picture_corner   }  } ... }

In one example, the signaling may be based on the following semantics:

Sequence parameter set { ... min_QT_split_for_CTU_edge_signaled if(min_QT_split_for_CTU_edge_signaled){ same_min_QT_split_value_for_all_boundary_CTUs_flag   if(same_min_QT_split_value_for_all_boundary_CTUs_flag)   {  min_QT_split_for_CTU_at_boundary   }   else   {  min_QT_split_for_CTU_at_right_picture_edge  min_QT_split_for_CTU_at_bottom_picture_edge  min_QT_split_for_CTU_at_rightbottom_picture_corner   } sps_slice_level_override_present  } Slice header { ...  if(sps_slice_level_override_present)  {  slice_level_override_flag if(slice_level_override_flag)   {  slice_min_QT_split_for_CTU_at_boundary   }  } ... }

In one example, the signaling may be based on the following semantics:

Sequence parameter set { ... min_QT_split_for_CTU_edge_signaled if(min_QT_split_for_CTU_edge_signaled){  min_QT_split_for_CTU_at_boundary sps_slice_level_override_present  } Slice header { ...  if(sps_slice_level_override_present)  {  slice_level_override_flag if(slice_level_override_flag)   {  min_QT_split_for_CTU_at_right_picture_edge  min_QT_split_for_CTU_at_bottom_picture_edge  min_QT_split_for_CTU_at_rightbottom_picture_corner   }  } ... }

In one example, the signaling may be based on the following semantics:

Sequence parameter set { ... min_QT_split_for_CTU_edge_signaled if(min_QT_split_for_CTU_edge_signaled){ min_QT_split_for_CTU_at_right_picture_edge min_QT_split_for_CTU_at_bottom_picture_edge min_QT_split_for_CTU_at_rightbottom_picture_corner sps_slice_level_override_present  } Slice header { ...  if(sps_slice_level_override_present)  {  slice_level_override_flag if(slice_level_override_flag)   {  slice_min_QT_split_for_CTU_at_boundary   }  } ... }

In one example, the signaling may be based on the following semantics,which may be included, for example, in one of a parameter set or a sliceheader:

{ ...  min_QT_split_information_present_flag  if(min_QT_split_informatiou_present_flag)  { min_QT_split_for_CTU_at_right_picture_edge min_QT_split_for_CTU_at_bottom_picture_edge min_QT_split_for_CTU_at_rightbottom_picture_corner  }  else  {   //infer values  } ... }

In one example, the signaling above may be included in a slice headerbased on a flag which is included in a parameter set and/or an inferredvalue.

In one example, the signaling may be based on the following semantics:

Sequence parameter set {  ...  sps_min_QT_split_in_I_SLlCE_for_CTU_at_right_picture_edge  sps_min_QT_split_in_I_SLICE_for_CTU_at_bottom_picture_edge  sps_min_QT_split_in_I_SLICE_for_CTU_at_rightbottom_picture_corner  sps_min_QT_split_in_P_SLICE_for_CTU_at_right_picture_edge  sps_min_QT_split_in_P_SLICE_for_CTU_at_bottom_picture_edge  sps_min_QT_split_in_P_SLICE_for_CTU_at_rightbottom_picture_corner  sps_min_QT_split_in_B_SLICE_for_CTU_at_right_picture_edge  sps_min_QT_split_in_B_SLlCE_for_CTU_at_bottom_picture_edge  sps_min_QT_split_in_B_SLICE_for_CTU_at_rightbottom_picture_corner  ... }

Where Each of the Example Syntax Elements

X_min_QT_split_in_Y_SLICE_for_CTU_at_Z indicates the minimum number ofQT splits to be performed for a corresponding CTU according to alocation and a slice type.

In one example, the signaling may be based on the following semantics:

Sequence parameter set { ... sps_min_QT_split_in_I_SLICE_luma_channel_for_CTU_at_right_picture_edge sps_min_QT_split_in_I_SLICE_luma_channel_for_CTU_at_bottom_picture_edge sps_min_QT_split_in_I_SLICE_luma_channel_for_CTU_at_rightbottom_picture_corner sps_min_QT_split_in_I_SLICE_chroma_channel_for_CTU_at_right_picture_edge sps_min_QT_split_in_I_SLICE_chroma_channel_for_CTU_at_bottom_picture_edge sps_min_QT_split_in_I_SLICE_chroma_channel_for_CTU_at_rightbottom_picture_corner  sps_min_QT_split_in_P_SLICE_for_CTU_at_right_picture_edge sps_min_QT_split_in_P_SLICE_for_CTU_at_bottom_picture_edge sps_min_QT_split_in_P_SLICE_for_CTU_at_rightbottom_picture_corner sps_min_QT_split_in_B_SLICE_for_CTU_at_right_picture_edge sps_min_QT_split_in_B_SLICE_for_CTU_at_bottom_picture_edge sps_mtn_QT_split_in_B_SLICE_for_CTU_at_rightbottom_picture_corner ... }

Where Each of the Example Syntax Elements

X_min_QT_split_in_Y_SLICE_Z_channel_for_CTU_at_N indicates the minimumnumber of QT splits to be performed for a corresponding CTU according toa location, a slice type, a color component channel.

In one example, the signaling may be based on the following semantics:

Sequence parameter set { ...  for (temporalID=0;temporalID<NumberOfTemporalLayers: temporalID++)  { sps_min_QT_split_for_CTU_at_right_picture_edge[temporalID| sps_min_QT_split_for_CTU_at_bottom_picture_edge[temporalID] sps_min_QT_split_for_CTU_at_rightbottom_picture_corner[temporalID] }... }

Where Each of the Example Syntax Elements

X_min_QT_split_for_CTU_at_Y[temporalID] indicates the minimum number ofQT splits to be performed for a corresponding CTU according to alocation and temporal layer value.

In this manner, video encoder 200 represents an example of a deviceconfigured to receive a video block including sample values, determinewhether the video block is a fractional boundary video block andpartition the sample values according to an inferred partitioning usinga subset of available partition modes.

Referring again to FIG. 13, video encoder 200 may generate residual databy subtracting a predictive video block from a source video block.Summer 202 represents a component configured to perform this subtractionoperation. In one example, the subtraction of video blocks occurs in thepixel domain. Transform coefficient generator 204 applies a transform,such as a discrete cosine transform (DCT), a discrete sine transform(DST), or a conceptually similar transform, to the residual block orsub-divisions thereof (e.g., four 8×8 transforms may be applied to a16×16 array of residual values) to produce a set of residual transformcoefficients. Transform coefficient generator 204 may be configured toperform any and all combinations of the transforms included in thefamily of discrete trigonometric transforms. As described above, inITU-T H.265, TBs are restricted to the following sizes 4×4, 8×8, 16×16,and 32×32. In one example, transform coefficient generator 204 may beconfigured to perform transformations according to arrays having sizesof 4×4, 8×8, 16×16, and 32×32. In one example, transform coefficientgenerator 204 may be further configured to perform transformationsaccording to arrays having other dimensions. In particular, in somecases, it may be useful to perform transformations on rectangular arraysof difference values. In one example, transform coefficient generator204 may be configured to perform transformations according to thefollowing sizes of arrays: 2×2, 2×4N, 4M×2, and/or 4M×4N. In oneexample, a 2-dimensional (2D) M×N inverse transform may be implementedas 1-dimensional (1D) M-point inverse transform followed by a 1D N-pointinverse transform. In one example, a 2D inverse transform may beimplemented as a 1D N-point vertical transform followed by a 1D N-pointhorizontal transform. In one example, a 2D inverse transform may beimplemented as a 1D N-point horizontal transform followed by a 1DN-point vertical transform. Transform coefficient generator 204 mayoutput transform coefficients to coefficient quantization unit 206.

Coefficient quantization unit 206 may be configured to performquantization of the transform coefficients. As described above, thedegree of quantization may be modified by adjusting a quantizationparameter. Coefficient quantization unit 206 may be further configuredto determine quantization parameters and output QP data (e.g., data usedto determine a quantization group size and/or delta QP values) that maybe used by a video decoder to reconstruct a quantization parameter toperform inverse quantization during video decoding. It should be notedthat in other examples, one or more additional or alternative parametersmay be used to determine a level of quantization (e.g., scalingfactors). The techniques described herein may be generally applicable todetermining a level of quantization for transform coefficientscorresponding to a component of video data based on a level ofquantization for transform coefficients corresponding another componentof video data.

As illustrated in FIG. 13, quantized transform coefficients are outputto inverse quantization/transform processing unit 208. Inversequantization/transform processing unit 208 may be configured to apply aninverse quantization and an inverse transformation to generatereconstructed residual data. As illustrated in FIG. 13, at summer 210,reconstructed residual data may be added to a predictive video block. Inthis manner, an encoded video block may be reconstructed and theresulting reconstructed video block may be used to evaluate the encodingquality for a given prediction, transformation, and/or quantization.Video encoder 200 may be configured to perform multiple coding passes(e.g., perform encoding while varying one or more of a prediction,transformation parameters, and quantization parameters). Therate-distortion of a bitstream or other system parameters may beoptimized based on evaluation of reconstructed video blocks. Further,reconstructed video blocks may be stored and used as reference forpredicting subsequent blocks.

As described above, a video block may be coded using an intraprediction. Intra prediction processing unit 212 may be configured toselect an intra prediction mode for a video block to be coded. Intraprediction processing unit 212 may be configured to evaluate a frameand/or an area thereof and determine an intra prediction mode to use toencode a current block. As illustrated in FIG. 13, intra predictionprocessing unit 212 outputs intra prediction data (e.g., syntaxelements) to entropy encoding unit 218 and transform coefficientgenerator 204. As described above, a transform performed on residualdata may be mode dependent. As described above, possible intraprediction modes may include planar prediction modes, DC predictionmodes, and angular prediction modes. Further, in some examples, aprediction for a chroma component may be inferred from an intraprediction for a luma prediction mode. Inter prediction processing unit214 may be configured to perform inter prediction coding for a currentvideo block. Inter prediction processing unit 214 may be configured toreceive source video blocks and calculate a motion vector for PUs of avideo block. A motion vector may indicate the displacement of a PU (orsimilar coding structure) of a video block within a current video framerelative to a predictive block within a reference frame. Interprediction coding may use one or more reference pictures. Further,motion prediction may be uni-predictive (use one motion vector) orbi-predictive (use two motion vectors). Inter prediction processing unit214 may be configured to select a predictive block by calculating apixel difference determined by, for example, sum of absolute difference(SAD), sum of square difference (SSD), or other difference metrics. Asdescribed above, a motion vector may be determined and specifiedaccording to motion vector prediction. Inter prediction processing unit214 may be configured to perform motion vector prediction, as describedabove. Inter prediction processing unit 214 may be configured togenerate a predictive block using the motion prediction data. Forexample, inter prediction processing unit 214 may locate a predictivevideo block within a frame buffer (not shown in FIG. 13). It should benoted that inter prediction processing unit 214 may further beconfigured to apply one or more interpolation filters to a reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Inter prediction processing unit 214 may output motionprediction data for a calculated motion vector to entropy encoding unit218. As illustrated in FIG. 13, inter prediction processing unit 214 mayreceive reconstructed video block via filter unit 216. Filter unit 216may be configured to perform deblocking and/or Sample Adaptive Offset(SAO) filtering. Deblocking refers to the process of smoothing theboundaries of reconstructed video blocks (e.g., make boundaries lessperceptible to a viewer). SAO filtering is a non-linear amplitudemapping that may be used to improve reconstruction by adding an offsetto reconstructed video data.

Referring again to FIG. 13, entropy encoding unit 218 receives quantizedtransform coefficients and predictive syntax data (i.e., intraprediction data, motion prediction data, QP data, etc.). It should benoted that in some examples, coefficient quantization unit 206 mayperform a scan of a matrix including quantized transform coefficientsbefore the coefficients are output to entropy encoding unit 218. Inother examples, entropy encoding unit 218 may perform a scan. Entropyencoding unit 218 may be configured to perform entropy encodingaccording to one or more of the techniques described herein. Entropyencoding unit 218 may be configured to output a compliant bitstream,i.e., a bitstream that a video decoder can receive and reproduce videodata therefrom.

FIG. 19 is a block diagram illustrating an example of a video decoderthat may be configured to decode video data according to one or moretechniques of this disclosure. In one example, video decoder 300 may beconfigured to reconstruct video data based on one or more of thetechniques described above. That is, video decoder 300 may operate in areciprocal manner to video encoder 200 described above. Video decoder300 may be configured to perform intra prediction decoding and interprediction decoding and, as such, may be referred to as a hybriddecoder. In the example illustrated in FIG. 19 video decoder 300includes an entropy decoding unit 302, inverse quantization unit 304,inverse transformation processing unit 306, intra prediction processingunit 308, inter prediction processing unit 310, summer 312, filter unit314, and reference buffer 316. Video decoder 300 may be configured todecode video data in a manner consistent with a video encoding system,which may implement one or more aspects of a video coding standard. Itshould be noted that although example video decoder 300 is illustratedas having distinct functional blocks, such an illustration is fordescriptive purposes and does not limit video decoder 300 and/orsub-components thereof to a particular hardware or softwarearchitecture. Functions of video decoder 300 may be realized using anycombination of hardware, firmware, and/or software implementations.

As illustrated in FIG. 19, entropy decoding unit 302 receives an entropyencoded bitstream. Entropy decoding unit 302 may be configured to decodequantized syntax elements and quantized coefficients from the bitstreamaccording to a process reciprocal to an entropy encoding process.Entropy decoding unit 302 may be configured to perform entropy decodingaccording any of the entropy coding techniques described above. Entropydecoding unit 302 may parse an encoded bitstream in a manner consistentwith a video coding standard. Video decoder 300 may be configured toparse an encoded bitstream where the encoded bitstream is generatedbased on the techniques described above. That is, for example, videodecoder 300 may be configured to determine an inferred partitioning forfractional boundary video blocks based on one or more of the techniquesdescribed above for purposes of reconstructing video data. For example,video decoder 300 may be configured to parse syntax elements and/orevaluate properties of video data in order to determine a partitioningfor fractional boundary video blocks.

Referring again to FIG. 19, inverse quantization unit 304 receivesquantized transform coefficients (i.e., level values) and quantizationparameter data from entropy decoding unit 302. Quantization parameterdata may include any and all combinations of delta QP values and/orquantization group size values and the like described above. Videodecoder 300 and/or inverse quantization unit 304 may be configured todetermine QP values used for inverse quantization based on valuessignaled by a video encoder and/or through video properties and/orcoding parameters. That is, inverse quantization unit 304 may operate ina reciprocal manner to coefficient quantization unit 206 describedabove. For example, inverse quantization unit 304 may be configured toinfer predetermined values (e.g., determine a sum of QT depth and BTdepth based on coding parameters), allowed quantization group sizes, andthe like, according to the techniques described above. Inversequantization unit 304 may be configured to apply an inversequantization. Inverse transform processing unit 306 may be configured toperform an inverse transformation to generate reconstructed residualdata. The techniques respectively performed by inverse quantization unit304 and inverse transform processing unit 306 may be similar totechniques performed by inverse quantization/transform processing unit208 described above. Inverse transform processing unit 306 may beconfigured to apply an inverse DCT, an inverse DST, an inverse integertransform, Non-Separable Secondary Transform (NSST), or a conceptuallysimilar inverse transform processes to the transform coefficients inorder to produce residual blocks in the pixel domain. Further, asdescribed above, whether a particular transform (or type of particulartransform) is performed may be dependent on an intra prediction mode. Asillustrated in FIG. 19, reconstructed residual data may be provided tosummer 312. Summer 312 may add reconstructed residual data to apredictive video block and generate reconstructed video data. Apredictive video block may be determined according to a predictive videotechnique (i.e., intra prediction and inter frame prediction). In oneexample, video decoder 300 and the filter unit 314 may be configured todetermine QP values and use them for post filtering (e.g., deblocking).In one example, other functional blocks of the video decoder 300 whichmake use of QP may determine QP based on received signaling and use thatfor decoding.

Intra prediction processing unit 308 may be configured to receive intraprediction syntax elements and retrieve a predictive video block fromreference buffer 316. Reference buffer 316 may include a memory deviceconfigured to store one or more frames of video data. Intra predictionsyntax elements may identify an intra prediction mode, such as the intraprediction modes described above. In one example, intra predictionprocessing unit 308 may reconstruct a video block using according to oneor more of the intra prediction coding techniques described herein.Inter prediction processing unit 310 may receive inter prediction syntaxelements and generate motion vectors to identify a prediction block inone or more reference frames stored in reference buffer 316. Interprediction processing unit 310 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used for motion estimationwith sub-pixel precision may be included in the syntax elements. Interprediction processing unit 310 may use interpolation filters tocalculate interpolated values for sub-integer pixels of a referenceblock. Filter unit 314 may be configured to perform filtering onreconstructed video data. For example, filter unit 314 may be configuredto perform deblocking and/or SAO filtering, as described above withrespect to filter unit 216. Further, it should be noted that in someexamples, filter unit 314 may be configured to perform proprietarydiscretionary filter (e.g., visual enhancements). As illustrated in FIG.19, a reconstructed video block may be output by video decoder 300. Inthis manner, video decoder 300 may be configured to generatereconstructed video data according to one or more of the techniquesdescribed herein. In this manner video decoder 300 represents an exampleof a device configured to receive residual data corresponding to a codedvideo block including sample values, determine whether the coded videoblock is a fractional boundary video block, determine a partitioning forthe coded video block according to an inferred partitioning using asubset of available partition modes, and reconstruct video data based onthe residual data and the partitioning for the coded video block.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Moreover, each functional block or various features of the base stationdevice and the terminal device used in each of the aforementionedembodiments may be implemented or executed by a circuitry, which istypically an integrated circuit or a plurality of integrated circuits.The circuitry designed to execute the functions described in the presentspecification may comprise a general-purpose processor, a digital signalprocessor (DSP), an application specific or general applicationintegrated circuit (ASIC), a field programmable gate array (FPGA), orother programmable logic devices, discrete gates or transistor logic, ora discrete hardware component, or a combination thereof. Thegeneral-purpose processor may be a microprocessor, or alternatively, theprocessor may be a conventional processor, a controller, amicrocontroller or a state machine. The general-purpose processor oreach circuit described above may be configured by a digital circuit ormay be configured by an analogue circuit. Further, when a technology ofmaking into an integrated circuit superseding integrated circuits at thepresent time appears due to advancement of a semiconductor technology,the integrated circuit by this technology is also able to be used.

Various examples have been described. These and other examples arewithin the scope of the following claims.

CROSS REFERENCE

This Nonprovisional application claims priority under 35 U.S.C. § 119 onApplication No. 62/693,325 on Jul. 2, 2018, the entire contents of whichare hereby incorporated by reference.

1. A decoder for decoding video data, the decoder comprising one or moreprocessors configured to: determine whether a coding unit is afractional boundary coding unit; infer a value of a first syntax elementto indicate that the coding unit is split, in a case that the codingunit is a fractional boundary coding unit, wherein the first flagspecifies whether the coding unit is split; determine whether the codingunit extends beyond the bottom-right picture boundary; parse a secondflag indicating whether a quadtree split is performed on the coding unitor a binary symmetric split is performed on the coding unit, in a casethat the coding unit does not extend beyond the bottom-right pictureboundary; and infer a value of the second flag to indicate that thequadtree split is performed on the coding unit, in a case that thecoding unit does extend beyond the bottom-right picture boundary.
 2. Anencoder for encoding video data, the encoder comprising one or moreprocessors configured to: determine whether a coding unit is afractional boundary coding unit; infer a value of a first syntax elementto indicate that the coding unit is split, in a case that the codingunit is a fractional boundary coding unit, wherein the first flagspecifies whether the coding unit is split; determine whether the codingunit extends beyond the bottom-right picture boundary; parse a secondflag indicating whether a quadtree split is performed on the coding unitor a binary symmetric split is performed on the coding unit, in a casethat the coding unit does not extend beyond the bottom-right pictureboundary; and infer a value of the second flag to indicate that thequadtree split is performed on the coding unit, in a case that thecoding unit does extend beyond the bottom-right picture boundary.
 3. Adecoding method for decoding video data, the method including:determining whether a coding unit is a fractional boundary coding unit;inferring a value of a first syntax element to indicate that the codingunit is split, in a case that the coding unit is a fractional boundarycoding unit, wherein the first flag specifies whether the coding unit issplit; determining whether the coding unit extends beyond thebottom-right picture boundary; parsing a second flag indicating whethera quadtree split is performed on the coding unit or a binary symmetricsplit is performed on the coding unit, in a case that the coding unitdoes not extend beyond the bottom-right picture boundary; and inferringa value of the second flag to indicate that the quadtree split isperformed on the coding unit, in a case that the coding unit does extendbeyond the bottom-right picture boundary.